Hello DavidP,
Sounds like your gearbox had all of the CP1000 upgrades done back in the day. The improved layshaft with circlip location of the high gear came into production late in the '73 model year, it was never part of an upgrade kit. Likewise, the mainshaft high gear has to be changed to the later one, as the bearing for the early type was supposed to be paired with the gear, and has been unavailable for eons anyway. Keep your fingers crossed on the Trident, but for the sake of a gasket and mainshaft lockwasher, I'd be having a look. I just did a quick strip/check of two 5 speed converted pre-unit boxes, and one of them was missing the circlip that locates the layshaft 1st gear dog - you just never do know what people will do in ignorance!

Last edited by TinkererToo; 03/21/21 1:33 pm. Reason: clarity