The gearbox for the v6 engine is a Vauxhall R25-R28 5 speed manual. Internally, it’s a Getrag 240 which is the same gearbox as used on other marques, most notably BMW. The final gear ratios are not too far different from the donor car however, with the MGB being so much lighter, a higher gearing is desirable. The gearbox is bearable on a 3.9 diff but you’ll find yourself pulling off in 2nd gear a lot of the time. It will be ideal for a 3.3 or 3.07 diff.
In comparison to the MGB box, it’s physically a little taller so needs similar modification to the car as you’d do for an LT88 or R380. It’s also not got any speed drive output (mechanical or electronic). The donor car took its speed pulse from the ABS sensors. This means that an alternative solution is needed.
Gear ratios are as follows:-