Other then the kick down shaft linkage...what is the difference between the a/c carb..the manual...and the automatic?

"a/c" Did you mean "AVS"? If so, AFAIK the auto has a long horizontle throttle pin (for the slotted kickdown rod) & a manual app has a short one

Some carbs had a blow-off valve between the secondary throttle bores, others did not (not sure of the exact applications - I'd have to look at all of mine). There were possible differences in metering rods and jet sizes and clusters may have also been different.

That would be correct.

AC carbs had hot idle compensators. Not sure if jets and rods, idle feed restrictions are the different between manual and auto, all have the same size throttle, ventura (340-383 one size, 440 bigger). I picked up a few more and I have a 69 383 manual and auto carb, I'll check for differences. One thing I found different, 68 383 stick has holes in the primary blades and the 69 doesn't. Looks stock, not buggered up.

Paging Scott Smith

Paging your service manual, which would detail all that out.

My 70 FSM shows a difference between manual and automatic AVS'.

It also lists, for autos only, a separate listing for with AC and without, but the specs are identical, they do have different part numbers, but that must be for the assembly WITH the idle compensator..

Supercuda (and others) pretty much covered it.

The question I would ask the OP is;

What are your goals in asking that question?

There are a lot of differences depending on application.