I've located a slant super six engine and the seller will sell me all the super six components. I have an automatic torqueflight in my Duster and want to be sure that I ask for all the components necessary to make the installation easy without additional purchases. Could someone direct me to a comprehensive listing of components? Or, if you're so inclined, list them here? Thank you much.

I'm guessing I need:
1. Intake manifold
2. Exhaust manifold
3. Carburetor
4. Air breather unit
5. Kickdown linkage from carb to tranny
6. Throttle linkage? (mine is currently cable).
7. Triangle washers

(1) Yes.
(2) No, unless you have one of the older designs with the triangular counterweight. Updating to a round counterweight design might not be a bad idea, and just having a spare good condition exhaust manifold wouldn't be a bad idea either.
(3) Yes.
(4) Yes.
(5) Yes, including the lever on the transmission.
(6) No, but would be nice to have just in case.
(7) No, unless you want a spare set.

You will also need the short metal fuel line that goes into the front of the two barrel carb. The first foot or so of the Super Six 2 1/4 inch exhaust pipe would also be good to grab to get the pipe flange with the larger inlet size. I would also grab the distributor, the complete choke thermostat assembly down to the exhaust manifold, and the throttle return springs and bracket (if present).

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Casually looking for a Clifford hyperpak intake for cheap.

May I ask why the distributor? Should be the same right? Mine is a 1974 and electronic.

What's the level on the transmission? So, the complete list is:
1. Intake manifold
2. Exhaust manifold
3. Carburetor
4. Air breather unit
5. Kickdown linkage from carb to tranny
6. Throttle linkage? (mine is currently cable).
7. Triangle washers
8. Metal fuel line from carb.
9. Exhaust flange.
10. Choke thermostat assembly.
11. Throttle and kickdown return springs and brackets.

You needn't change the exhaust manifold no matter what shape the heat valve counterweight is. The factory 2bbl choke thermostat will bolt directly onto any '73 or later exhaust manifold, and the (nicer, adjustable) Electric choke kit #1232 will bolt to any exhaust manifold, period. There is no difference is size or flow of exhaust manifolds for 1bbl vs. 2bbl.

Shorter throttle cable, completely different kickdown linkage assembly (all rods, pivots, brackets, etc. including the lever on the transmission's kickdown shaft) -- yes.

"Air breather" -- no, the breather is the round device at the top rear of the valve cover. You need the 2bbl air cleaner assembly.

Carburetor: Yes, of course.

Triangle washers: Never hurts to have spares, but they don't differ 1bbl vs. 2bbl.

Your existing 1974 1bbl fuel line will hook directly to the 2bbl carburetor since both your present 1bbl and the 2bbl carburetor have the fuel inlet on the front. However, you'll want to do the Fuel line mod.

Distributor: usually a better advance curve on the units that went with the 2bbl carburetor. At this late date who knows what distributor is on the source engine, but it never hurts to have a spare.

It is very much worth your while to get the good gaskets for the manifolds-to-head and intake-to-exhaust junctions.

And you'll want to go through the carburetor and hope it's not a "remanufactured" piece o' junk. New ones are readily available at the moment (but move fast; availability of these is a "sometimes" thing). Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.

If the Super Six you're looking at has an aluminum intake manifold (see if a magnet will stick) then check it very carefully for cracks in the floor area, and there'll be some special prepwork before installation to make sure it does not create vacuum leaks.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Whoops! Typo. I meant "leveR" on the transmission.

The kickdown rod attaches to the kickdown lever on the transmission. These changed based on application, so if you can, it is nice to have the correct Super Six lever. However, as Dan points out, at this late date, who knows what is on there. Someone could have swapped out the transmission and it no longer has the correct Super Six piece.

I have read that the older triangular counter weights were more prone to seizing, but if yours still turns freely, then don't worry about it.

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Casually looking for a Clifford hyperpak intake for cheap.

Possible but relatively unlikely compared to a carburetor swap.
Pre-1970 counterweights were rectangular. 1970-up are round and yes, generally less prone to seizing. OP's car is a '74, it sounds like.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks much gents. I must admit, I'd rather have a V8, but the slant six is unique and has become a challenge for me. I just want a little more pep! I suppose changing the gear ratio in the rear end to 4.x:1 would help with that too. Here's my car--if I may.

A 4.x ratio in the rear end would be a "pain in the rear" after an hour or so of fun. Unless you're planning for a top speed of about 45 mph.

You'll hear the name "Clifford" come up, but be very careful before you decide to spend any money with Clifford. They have a long and ugly reputation for being a bunch of clowns; see for example here, here, here, here, and here. Much of what they sell is inaccurately described, and a lot of it is not even slightly cost-effective. The good news is that you don't need to go to Clifford to get hot rod parts for slant-6s; there are lots of other, better options. See for example Dutra Duals and header options discussed in this thread and this one, Erson custom cams, HEI ignition upgrade, Mike Jeffreys windage trays, Hurricane intakes, other exotic intakes. Hi-perf engine buildup here, high-perf parts and build info here.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.