I recommend not regrooving the hi/rev drum as one of the steel plates can hang up in the old groove but I guess if the clearances are closely checked one might get away with it. For a street trans I find a 4 clutch drum [single ID groove] and cut down the thick backing plate to a similar shape of the forward clutch bevel spring plate and sneak in an extra clutch. The 4 clutch low is doable as all it does is release in "manual" low [the sprag clutch does the same thing in "Drive", it doesn't have to stop a heavy drum like the band does or the hi/rev drum. With the torque and hp the poster was looking for the engine may overpower the low gear clutch. An extra clutch will provide about 20% more holding power.John I. said:You can do the 5 clutch thing for a few bucks at a machine shop. Raise the snap ring groove in the one clutch pack and machine the end plate down in the other one. (It's been so long since I've had the reliable old thing apart, I can't remember which one I did which to...) :lol:
My low reverse only had 4 clutches, and I just left it the way it was, and I've never had any trouble with it, but maybe I've been lucky.