Picked up a low mileage (51k) '73 225 a couple weeks ago for $300. I've removed the head and taken it to the machine shop for shaving. Everything else looks pretty clean and solid. Installed a Oregon 2106 cam and new timing chain. Plan to do some minor cleanup porting on the head and lap the valves in. Once together it will wear a Super six intake/Weber 38DGES. Using the stock exhaust manifold that has been ported out a bit flowing into a 2.25 exhaust.
I measured the block and pistons are about .180 in the hole and head chambers are about 60ccs. Told the machine shop to take .100 off the head. Sound about right? I'm shooting for 8.5-9:1 compression. With .100 off the head, should I use washers on the head bolts? Anything I'm missing?

What disassembly and checks/measurement have you done on the short block? Yeah, it might have low miles, but it has high years (most of half a century) and stuff deteriorates from sitting unused. If the rings are stuck or otherwise degraded/the cylinders need attention, putting a nice fresh head atop them stands a good chance of making the engine burn a lot of oil. Also, there's likely quite a bit of sludge in the oil passages and rust/mud in the coolant passages (where you can't see, even if the exposed areas look clean).

Plus, you may very well want to take some or most of your deck surface off the block rather than the head.

It will also be a good idea to service the oil pressure relief valve to make sure it's doing its job, as described in these two threads: thread 1, thread 2.

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As far as inspection, when I pulled the valve cover and oil pan, everything was pretty clean. A small metalic film at the bottom of the pan but nothing major and no sludge or crusty oil build up. Coolant came out clean and green and I see very little corrosion. Cam and cam bearings in good shape. Lifters slid right out with no fuss. Oil pump is clean inside and gear appears to be in good condition. I plan on pulling it apart and servicing the oil pressure valve. Inspected cylinder walls and no streaks or scars other than a small ridge at the top. This is why I don't plan to disassemble the bottom end. The new cam and head shave should wake it up and should last me a while ( I hope)
Is .100 off the head a problem? I've read several places that is a good amount based on my measurements.

Also forgot to mention that I heard this engine running. Was on the road previously. Ran well but made a little valve chatter from lack of adjustment. Was out of the car before I got it so didn't have a chance to do a compression check. If you haven't guessed, hoping to have this on the road soon for cheap.

I would put the combustion chamber cc size, piston recession, head gasket compressed thickness and diameter in an online compression calculator like the one at the link below and know the compression ratio that I was building to rather than ask if .100 off was correct for my build.

https://rbracing-rsr.com/compstaticcalc.html

The .180 piston recession is in the ball park, at least I have seen that on one of my motors. The 60 cc stock head combustion chamber is larger than any that I have ever checked.

And I have seen folks on online forums recommend cutting the block instead of the head. But I have never seen a reason why one should be preferred over the other.

When both the block and head are available for machining I have always done a light clean up cut on the block, installed the pistons I was using in 1&6 with the completed crank and rods to get the final piston recession value then had the head cut to get the exact combustion chamber size and compression ratio that I was after.

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https://www.youtube.com/watch?v=uX8Nj8ABEI8

I checked two different chambers on the head and got 60ccs. (#2 and#5) Using the calculator, originally it had about 7.6. With .100 off the head it should be about 45ccs and should give me 8.9. Sound about right?

Efficiency is lost with the piston landing so far down the hole like most Mopars do. Most slants are around .180" down the hole. Unburned fuel mixture hides in the area between the piston and bore from the piston top to the ring land. The higher up the piston lands, the less opportunity that fuel mixture has to hide.

Also, the area between the fire ring in the head gasket and the edge of the bore between the deck and the head is another hiding place for unburned mixture. This is one reason why a thinner head gasket is better than a thicker one.

All of this leads up towards the "zero deck" theory, where the piston is brought up even with the deck at TDC. A common compressed head gasket thickness is .037-.040." The minimum clearance from piston top to head surface is usually around.035-.040" so zero deck works out perfect for most motors with a conventional composite gasket.

Motors like the slant where the cylinder bore more or less continues into the chamber area of the head can utilize negative deck, where the piston actually "pops up" past the deck at TDC. Attention has to be paid to the height of the ring lands in relation to the top of the bore.

Some heads have or can be cut to have a flat "quench" area in the chamber. In this case it can be advantageous to cut the head. In many instances the cut has to be split between the head and block deck to optimize the position of everything for the particular combination of parts being used.

In some instances (like on a slant) there is enough meat everywhere to cut anywhere to clean up whatever surface might need it without really changing anything too much to worry about...