You think that getrag would mate up to an LS9 anytime this century? Fuck no. Everything's completely wrong for that. Bellhousing pattern, depth, input shaft, spline count, everything. Not even close. Besides that, the LS9 would shred it a new asshole even if it did. I'd end up putting as much money into it to beef it up to the point it could handle 600FT Lbs as I would spend on an off-the-shelf ZR-1 spec Tremec T-6060.
If i went the LS9 route the getrag gearbox would be dead weight to me. Wouldn't be worth spending the money to modify it to fit and withstand the torque when the same dosh would buy a ZR1-spec Tremec six speed with double overdrive that's designed for that very engine in the first place. I'd only consider keeping it if I went with a Jap V8 that stands half a chance of mating up to it, though I'd still end up spending a bit to beef the internals up. I'd do at least 500HP 500FT LBs.
Drag racing sucks as far as specators go. It's six to fifteen seconds of engine noise followed by ten minutes of commercials and fucking announcer blabble. I'd honestly rather watch Nascar.
Oh, and I suppose F1 teams are derp for using 7-speed boxes, right? They've got 800HP and 500KG cars, better power/weight than that big block Chevelle at the drags. By your logic they should be using two speeds too. Or at least four speeds, given FIA regs, they're allowed a minimum of four speeds up to a max of seven, plus reverse. But no, they've got seven speeds, and they're the fastest racing machines that are worth watching, able to regularly pull 5Gs.