All early Minis and even the original Cooper "S" had a 4-speed gearbox that only has synchros in the top three gears. The 3-synchro gearboxes have smaller shafts and bearings, so a good idea to replace this layshaft, specially for bigger engines.
This shaft is not stepped like the 4-synchro versions. The outside diameter is the same for it's full length. Also a VERY god idea to relace the laygear bearings. Takes two of the 88G396 roller bearings, one at each end of the laygear.