I am right at the point of putting together a new motor for my SLC. I am going up 100hp from 435hp/350sbc to a 535hp/406SBC. I called up California motorsports who built my G50. It is upgraded with all the good parts available for a G50 to make it stronger, side plate, steel synchro, and better gears when I changed ratios. I asked Rodger how much power I could put through my GRBX and he looked at my build sheet and told me he was comfortable with 525 ft/lbs. The car weighs 2500ish, runs Hoosiers, and has a Quaife TBD in the GRBX I will tune my motor on the engine dyno to that number. The smaller diameter 7.5-inch R&P in the g50-01-03s is the limiting factor whereas the 9-inch G50-52 is quite a bit stronger.
So that is what I can tell you about a well-built G50 run as a track car GRBX. If I was doing your car with a Porsche I think I would be looking at a G50-52 or a 930 which also uses a 9-inch R&P.
What about the offroad Porsche-derived GRBX's like the Fortin, Albins etc,
www.fortinracing.com
weddleindustries.com
Then there are the $$$$$$ race stuff
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Holinger MXT 6 Speed Sequential Racing Transaxle
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