What crank 1970 318?

For instance, in 1966 a 273 balancer (all transmissions) part# 2658458 is the same as a 318 poly with a manual transmission. The 318 with and automatic is part# 2658459. All these cranks are forged. In 1968 all the 273, 318, and 340 engines use the same 2658458 balancer that the earlier 273 and manual trans 318 use. In '68 the 273 and 318 cars used a cast crank, but, the 340 crank is forged. I have no idea why a 318 poly with a manual trans would be different. It's internally balanced like all the others and the balancers look the same physically. I have seen a few varieties of the outer ring of some stock balancers. Some have flat front and back surfaces and some have a concave curved surface on one side.