I've heard of an "A" pump, but never seen one.

A "B" pump has a split bowl. Maybe that's what it is, I don't know.

The "B", in that position, {12JA-B-H} usually designates a "B" impeller, Not usually the best choice for a stock Olds.

Most Olds Had an "A" impeller, and some with an "A2" impeller. You can put as much HP as you can afford in front of it. 

Pics would help

And welcome to the madness.

Dan'l

Thanks for the reply, I will send pics later.
It is a split bowl.If i got it correct, would a "B" pump have a "B" impeller?
Sorry for lame questions, its all new to me.
Its all good madness on SCJB.

JA
JB
JC
JE
JF
JG
JI

These are the pump model

Any one of these can have an A2, A, B, C... cut impeller in it.
The letter in the tag is what it was shipped with, in 1976. Mine was shipped/built with an "A", (1976 also) and has had a A2 for 15+ years.

Dan'l

there is a lil more to it than that.

Also depends on use of the boat.

Knowing whats in the pump is important, too.

thats where i'd start.

Dan'l