You can cut down a torque convertor to use the ringgear only.
I wouldn't use a complete torqueconvertor for balancing reasons. The insides won't be held centered because there's no transmission input shaft.

I mounted a neutral flywheel against the B&M balanced flexplate and used slightly longer bolts into the crank flange.


I build mine from a spare cart and some scrap metal.
Here it is with a 360ci Small Block installed;