Thanks Grigg, I cleaned it off yesterday and found these numbers:

On a very rusted tag between two flathead screws "1308"

On another rusty tag "CON1/5" (numbers hardly legible)

On another rusty tag "1278"

Stamped GM3 591568 (Top of transmission)

Stamped 3 GM 591665 (side of transmission)

This transmission does have what looks to be a removable sideplate for a power take-off. What is the shift pattern on a 5-speed? I can try running through the gears to confirm?

I'll look to download and send photos when I get near my computer. I'm working off handheld

Thanks gents

1947 - 3800 dually known as "Deadwrench"
Link to a few photos

In this world there are givers and takers. The takers eat well, the givers sleep well.