The
LA 360, the 5.9 Mag and the cat crank 340 all have different amounts of factory imbalance required. It's not one size fits all.

Also, the transmission IS a one size fits all as long as it's either a smallblock bolt pattern or bigblock bolt pattern. The converter does have to match the splines on the transmission input shaft and the flexplate and the converter need to have the same bolt pattern but aside from that, the engine determines the amount if any factory imbalance needed on either flexplate or converter.

Example: A 318 is bolted to a '73 340 transmission. The converter and flexplate are neutral balance.
An LA 360 is bolted to a '73 340 transmission. Converter and /or flexplate needs the 360's amount of factory imbalance on either converter or flexplate.
A 5.9Mag is bolted to a 1973 340 transmission. The flexplate or converter needs to have the 5.9Mag factory imbalance 9on either flexplate or converter.

But you probably knew this.

R.