Sorry I went silent, I had a little setback:
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Apparently I was wrong when I said I got the car to dead hook once before. I found a good piece of asphalt and the car hooked for real this time, picked up pretty good, and took off harder than ever... then ~50' later the all too familiar sound of parts breaking came! Oops!
I'll chalk this up to $4!+ happens. My dad had bought this 3rd member used and I just put new bearings, seals, and clutches in it, double checked the pattern, set the bearing preload, and all *seemed* well (I've set up a few dozen ring & pinions before.) For all I know, it could have come out of a bazillion horsepower car.
Since I'm buying new gears anyway, I'll go to 4.30's since that's what my dad really wanted. It should help a tiny bit with reducing wheelspin off the line (which may not be a problem afterall!) and it'll give a little more wiggle room with rpm if the car ends up running faster than I've been planning for.