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It is actually a very realisitic power number for an engine with accessories, exhaust and functional air intake modeled. My buddies truck made right at 350 whp and 310 tq through a 4L80E and an 8.5 10-bolt. It had a LQ4 with ported and milled 241 heads, larger cam than mine, long tubes and TBSS intake with a 90mm TB and 4" air intake.
The L31 will make ~50 ft/lbs more down where the converter stalls at 2,000 rpm than the 6.0L did. Had a 1980 C10 with a cammed 305 Vortec/TH400 and 3.08s that was low 14 second truck. Same engine in my 1980 Corvette backed to a TH250 and 3.07 gear ran a 12.5 @ 110 mph in the 1/4. I really like the TH400/4L80E gearing myself but the LS is a terrible fit for it. There were tons of GM trucks and vans that came with a TH350 or TH400 and 3.08s. They cruise nicely on the highway.
Sorry, I hardly believe that at the crank, much less the wheels with a mild truck oriented camshaft, truck intake manifold. Have to remember an automatic sucks 20-25% of the power. My Hemi was also the same deal. 345 hp rating at the crank. With 1-3/4" long tube headers, exhaust, and tune and it only made 285 whp and 301 wtq.
I could see those kind of numbers in a car, with a manual trans and car intake manifold. A lightweight car also allows for more agressive tuning than a heavy truck which will add a bit more power as well. Have to keep the timing a bit lower and the fuel a bit richer on a street driven truck.
