I've never felt that welding weights on is a good idea. GRAMS as in fractions of grams, make a difference in engine balance.
I'd say buy a B&M or similar aftermarket flexplate which has the necessary balance built in. That way, you can use a "neutral balance" converter, which makes your selection broader, as well as being able to use that converter if you ever change to a different engine balance situation.
I have a factory 360/ 727 in mine, but when I get a stall converter, I've already got a BM flex to go in there.