What model auxiliary transmission Is it? Unless it is huge (as many were) then go for it, and price sounds great!
Brown Lipe was a brand name before Spicer bought/merged with them, that's where the nick name "Brownie Box" came to be and stuck for "auxiliary transmission". Watson is another old brand, Spicer also assumed their line.
Very very unlikely it has two overdrives and one under, I know of none. Most likely to have an under, direct, and over. Some don't have overdrive though, so be sure you get what you need.
The Spicer model numbers could be 5831 or 6xxx and after that the 7 and 8 thousand and even 12,000 model numbers are quite large, more than I'd want in one of these old 2 ton trucks.
I have a 6041 four speed for one of my trucks, going in a 1 ton and almost too large for that.
