Damaged crank flange

The bolts not only retain the flywheel or flexplate/TC, but also firmly clamp them onto the crank flange. That becomes more important as you get to higher power and higher RPM's and the torsional crank vibrations start to emerge: loose bolts there will worry out the threads/hole. But if you are just foolin' around with this engine, you can probably get by with it. Or put in a 5/16" dowel and matching tight fitting hole in the flexplate flange nearby.

Imagine taking a chunk that size out of the big end of 1 rod on the 7-8 journal.... that is what you are talking about with balance change. It will have maybe 1/3 or 1/4 of the effect of the weight on the TC of external balance 360, since it is about 1/3 to 1/4 to distance from the center line.

So not trivial but not huge if this is just a 'foolin' around' engine. You could tack about 1/4 to 1/3 of the weight out on the TC at the same crank angle and make up for it.

I like your engine parts combo. That is clever thinking for a low buck 318 stroker. How many cubes is that?