I have a 78 motor will my 68 904 tranny work with it? Also will a locking converter tranny work with the 78 motor? And Were can I find a 2800 rpm stall converter for a locking tranny?

Yes, a 68 904 should go right up to a 78 225. The 78 often (usually?) came with a lockup convertor, so no problem there either. I'm not aware that anyone makes a lockup convertor that would stall at 2800 behind an average slant. There's no aftermarket support for lockups.
Are you trying to decide which trans to use? What kind of driving will you be doing (street or race)? How stout is the engine?

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"A mechanic is Somebody."
- Jim Preston

Well here is my thing. I just finished puting my motor and electrical systems together I have a 68 tranny that needs a rebuild I have a 2800 rpm converter for it. The tranny that came with the motor(78 locking) was rebuilt about a year before it was pulled. I just want to put the car together and drive it and brake in the motor. I do not want to wait for 1 or 2 months to build the 68 tranny(money problems). As far as the motor My engine builder says close to 300 hp at the crank(we will see) rough stuff 600 cfm 4bbl clifford shorty intake w/ split headers ford 300 valves max ported head 9.1 compression .060 over bore roller rockers .5 lift 224@50 duration plus a few other tricks.
As far as driving this is a resto project weekend cruizer will see the strip once in a while.

The lockup trans will get you on the road, but that cam isn't going to be happy. Mix a low stall/lockup convertor and emissions shift schedule (read early) with lots of duration and you'll have a dog off the line.
Low gears will help - what have you got in it?
Can you afford a shift kit?
Make sure the k/d is up to snuff.
As a crutch, block off the accumulator and bump up the line pressure a tad; this will firm up the shifts and raise the shift points a bit, but you really do need that high stall.

_________________
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"A mechanic is Somebody."
- Jim Preston

I have a 3.21 I think its that or a 3.23 I think this tranny already has a shift kit but I do have one on the shelf just in case.

If the car is pretty light (68 yes, 78 no), those gears are about as tall as you'll be able to get away with. High 3's/low 4's would be ideal, but give it a shot and let us know how it does.

_________________
O==\=/==O

"A mechanic is Somebody."
- Jim Preston