First, are you planning on putting the A-code in the '91? Some states prohibit older engines in newer platforms as part of the smog laws. Plus you probably wouldn't want a three speed in a '91 although it would be cool to be different.
Back to your question; depends on the shape of the block and crank. For example, does it need a rebore? Do the mains (and rods) need to be align honed? Probably you would want to drop the compression to around 9 if carb'd (and if you need a rebore -- you'll need new slugs anyway). I had a '67 A-code. Had to run premium in it and back the timing off just so it wouldn't ping which slowed it down. If you can get by with rings and bearings, you can do a decent build up with a Performer RPM (or similar) intake, a Performer carb (I stay away from Holley's -- too "high maintenance" in my humble experience) a bigger cam, open air cleaner and electronic ignition. Shouldn't cost too much. If you need to do a full up rebore, it would be in the $1,500 range between the block and the heads. Might be cheaper to do the '91 block since it is roller (I think).
