So I've been searching for hours on this and thought we could put together a body of knowledge on the large bore saginaw boxes similar to what AGR uses. I know J10s and J20s had them. 3 3/8" piston bore.
I've also seen that:
1999 Dodge Dakotas and Durangos have them.
Dodge RAM 2500s and Chevy 2500s.

Can other confirms other vehicles which had the large bore gearboxes?

Many of the 60s Cadillacs and I believe some of the Hummers have the large bore box. I used one out of a Cadillac.

Anyone else? Come on, help out the poor man....

you sure about the J10 boxes????

Not 100% because I haven't personally pulled one but I've confirmed via several forum searches. If anyone could verify that would be great.
Right now I'm fairly confident about: J10s, J20s, 1999 Dodge Dakotas & Durangos.
Others: Ram & Chevy 2500s (years unknown), 60s Caddys, Hummer (H1?)

you sure about the J10 boxes????

I bought J20 box last week and they mistakenly gave me a J10 box at first which had smaller piston.

Btw, the '76 J20 box is still available from part store, it's a large bore, 4 bolts, 4.25 turns, 13/16 input, flare fitting. The part number is A1-Cardon 27-6529. I've just bought it last week from Winchester auto parts in San Jose.

/td