So the LS6 at 425hp was the top auto option?
Any recommendations as to what would add specific amounts of hp?
In addition, without having to rebuild the rear end, do we know what the hp the engine could be safely taken to on an auto?
OK, so mines a manual so a different set of potential 'abuse' issues - but I am running more HP (and importantly torque) than any high output 454 or perhaps even the legendary L88 engine (albeit at lower rpm's). The drive train is 100% stock - other than clutch. The rear end ratio is 3.08. Rear tyres additionally with 285 mm section have far more grip than any 1970's options (other than perhaps slicks).
I can report that I am still running all the original drive line components - all this with a very real and genuine engine dyno figure of 571 bhp and 606 ftlbs torque.
However - I never do a 'rev and drop the clutch' type pull aways. I do not do rolling burn-outs. It is this kind of treatment whether in an auto or manual that kills driveline components. Even something simple like ironworks on the carriageway allowing one wheel to spin-up momentarily (and then grip) can play havoc with driveline components.
As to whether an automatic transmission is 'kinder' on driveline components I'll leave for you to consider. Torque multiplication of the converter may well increase stress on components.