Help ID a tranny off of craigslist

Find neutral. Then take a wrench on the front shift shaft (3/4) and turn it RIGHT (CW). That is 3rd gear on a 4 speed, OD gear on an OD gearbox. Then just turn the input shaft ONE turn and watch the output.

If the output turns LESS than one turn with the input, it's a 4 speed

If the output turns MORE than one turn with the output, it's an OD

Turning the shaft LEFT (CCW) will be 1:1, or straight through, on EITHER a 4 speed or OD.