Welcome to FBBO from NorCal Sierras
V8 all the way
a couple options, depending on budget & availability
BUT;
I'd go with a BB, 440 if you can find a good one
383's are cheap enough too, there's plenty of them out there
they can hold their own
I really like the Low-deck B-series engines option
or a stroked Low-deck B series 383/400,
a 440 turned RB crank mains & counterweights
426/451+ cid that combo also has a
bit more room
for headers, exhaust, starter replacements, etc.
(
probably be able to keep your existing org. 273 torsion bars with the lighter engine too)
more room than the RB block does too
lost of affordable parts to do it too
can you tell I like Cubic Inches ?
If you're gonna' go racing, bigger is better
for just a tire shredding
street beast
IMO any well adorned, well tuned MoPar V8 will do, SB or BB
or a stroked SB, 318/390 360/408 (340's are a bit pricey)
hell even a well adorned std cid SB will roast the tires too,
even a well equipped 318 will too
there's lots of Magnum series SB's too 5.2ltr 318cid/5.9ltr 360cid
Magnum heads flow a little better than the earlier LA series too
already have hard seats, convert it to a carb & std ignition set up
is easy too (electric fuel pump required unless modified)
lots of reasonable crate engines choices too
just be careful if you go that route, do your research
any V8 with a good converter & proper gears behind it
can really improve performance
(even behind a 318 or 273, IMO go bigger the better)
If you go thru all the trouble to put a V8 in it
IMO, then do the most you can within your budget,
as many cubes as possible
these heavy cars like torque to get them moving
or roasting the tires
good luck