Mines from a '70 Vette, "sticker" rated at 390HP on the aircleaner. Never have looked at Tq specs for it, I'd guess in the 450-475 range? INternally my engine is still factory, heads were off once for a valve job, minor port clean up and I run the old Edelbrock intake that equivalant to a Perfromer now I guess, along with a Holley 780 vac secondary carb
I think the LS6 from the same year had 11:1 CR and somewhere in the 450/460HP range, mines 10.25:1, in '71 I think the LS6 dropped to about the same as the 70 LS5. Chevellles were probably rated lower just so GM could get the Vette as "Top Dog" in performance numbers.
The only thing holding back the LS5 from '70 is i'ts way under cammed (and real lazy ramps) for the CR, but back then with leaded higher octane gas, there wasn't any issues. The heads flow real good for factory, exhaust with the long castiron manifolds flow as good as shorty headers do. Just a decent cam with faster ramps, even leaving it flat tappet, would yeild another 40-50 HP and still idle like a Honda.
Besides, I shouldn't have made fun of your 250, I still run a 235 in my '59, and wouldn't pull it for a V8 swap unless I was forced to
