small block to big block

Many posts on this, use the Search. Need special motor mounts, different transmission, driveshaft, maybe a different rear end, maybe an aluminum radiator, stiffer torsion bars if a street driver. Headers often need a cutout in the fender wells. If not, the exhaust is choked so much the BB doesn't make much more power than a SB. The result is hard to handle on the street and most people do it to make a drag racing only car.

it's expensive, but if you get a bolt in front end (hemidenny makes them, or you can buy alterkation from rms) it will handle BETTER than originally, particularly if you build the BB with aluminum heads/intake.

the BB will weigh as much at that point as a stock SB, and the torsion bars are long gone (more weight gone) and you will have a modern suspension.

you will need a big block 727 auto trans or a big block bellhousing/manual trans

as far as power you can bet the BB will attain higher HP levels easier than SB (there is no replacement for displacement)

yes you can built the chit out of a SB, but BB heads flow more and you can put a lot more cubes in a BB (up to 572c.i.). you can get even get 500 to 600HP out of a BB without a stroker kit

so it's actually cheaper to get 500HP or more out of a big block than with a small block in the long run.