Re: relative strength of 9" vs 8&3/4" diffs
Okay, first things first. A 9" does not take 30hp more to turn. This is bollocks. Vl diff gears will fit, but I wouldn't try to run more than 450/500fwhp through them. Anthing more than 650fwhp is going to push the friendship with a BW 75 or 78 series diff, regardless of gears used. At the upper limits, gear strength is not the issue, you are risking outright hemisphere or axle failure. Hydratrack are good in theory, but can be troublesome in use. They use a special coupling to join the axles together instead of the usual cones, and thus require special axles.(and hemisphere, of course) What application is the car to be run in?
If you're not driving a manual you're really just steering.