There were five different gearboxes used in the MGA over the years of production, three different propshafts, two different starter positions in the bellhousing, two different clutch disks. The gearbox number can be found stamped on top of the gearbox next to the oil level dipstick. This is not very easy to get at, as the oil fill hole and dipstick is accessed through a hole in the top right side of the tunnel under the dash. Good luck in finding a good line of site to read this number without disassembling something major. If you can get there, it will look like the picture above. These are simple serial numbers, not containing any extra characters to designate the specific model of gearbox, so unless you have a comprehensive cross reference list you will have to judge by the appearance of the parts. Find that discussion in the Gearbox Tech section. All original units were manual 4 speed with three synchronized gears, non-synchro 1st and reverse gears. There was a moderately rare close ratio gearbox most often found in the Twin Cam or 1600-MK-II Deluxe cars. The gearboxes have been swapped out at least as often as engines, so don't count on having the original unit.