with out a looky see, no telling what is has been done to it since 1971.

all that is need is the correct size stock flex plate to install what ever size TC you want.

with a external balance TC you want the correct weight on the TC.

for example, I used an external balance TC from a 400 B engine on my external balance CAST CRANK 440.

IIRC, 383/400/440 cast crank share the same weight on TC.

I keep a few small & large flex plates for swaping TC around as needed. they all interchange and are 2 sizes.

IIRC,remove dust cover and you may tell by the starter ring gear, if it is thin it is the large TC and if it is thick it is the small TC