3 spd OD
A good one for that would be the 3 spd OD used in Ford Pickups and some cars like the Maverick, in the 70's and 80's. It was a modified version of the Ford Toploader 4 speed. It comes in two styles, external and internal linkage, as well as both steel and aluminum casings. What they did was to convert 3rd gear in the 4 speed into an overdrive, and then flip the shift linkage for 3-4 upside down. These are a pretty good transmission, and will stand up to a lot of abuse. They do use a floor shifter, BTW.
You will need an adaptor plate, as it wont bolt up to your stock bellhousing. The shift into overdrive is done manually, there are no electric or vacuum controls on the OD.