A/B Body 4 speed inside differences?

I have an iron case O/D A833 from a truck (B body) and an aluminum case O/D A833 from an A Body.

I was thinking about using best pieces from both and making one.

Before I tear into them...

Question is: Are the guts the interchangeable? Any differences in gears, etc.?

Are the aluminum cases really that prone to fail? I'll be running the 4 speed behind a slant six...currently with a 2.76 rear.

Thanks