Bandit, I ran a 56a 5 speed behind an A14 that made 100 hp at the rear wheels, through 8 inch wide slicks with sticky rubber at the drags in the mid 80's. It survived the abuse, but what killed it was my ignorance. I didn't recognise the sound the input shaft bearing makes when it's worn, so it eventually locked up & destroyed the input shaft, the cluster gear & the 3rd gear. This bearing only really gets splash lubrication, so when the oil level dropped a little, the bearing wore out. If I'd simply put new bearings in, I'd have been fine. So from experience here are some things I'd recommend. First, a good transmission fluid, I used Castrol Syntrans 80-90w, but any good synthetic should work. Secondly, overfill the box a bit, so theres some oil getting into that bearing.Thirdly, as soon as you here noises from the box, put new bearings in it. Any bearing dealer should be able to get you new ones, just get the numbers off the old bearings. Thats all I did when I needed to rebuild a gearbox. I ran one of these boxes in my 1000 hillclimb car behind an A12, with the Syntrans, for 2 years without breaking it, though I did get new bearings fitted over the off season. Also, there's some little screws in the sandwich plate. These control the shifter feel. I'd recommend screwing them in a little, or you'll be grabbing 4th gear when you're going for 2nd, or 1st when you're going for 3rd. Enjoy your new gearbox, & remember, 1st to 2nd is now Push forward,relax, then Push Forward again, letting the spring loading take the gear stick across the gate. Works every time.