8:1 and a plugged up head seems like a lost cause.
I can give you a little anecdotal information, since you stubbornly refuse to build a stovebolt to see for yourself. Back in the early 1960's I was a pit crew member on a team where we ran two supposedly identical 46 Ford coupes in the "stock" division at the Nashville Tennessee fairgrounds race track. Our only competition was a local body shop that sponsored a 52 Chevy coupe with a 261 engine (They were cheating, but so were we.) The 261 was an illegal engine since it was a "truck only" application. They tried to skirt the rules by calling it a "Canadian Pontiac" engine. They had about a 20 cubic inch advantage over our engines, since the "239" flathead engine could only come up to about 250 cubic inches with an .080" overbore. (Max the track rules allowed) The .080 over 261 was noticeably bigger.
Despite the displacement difference, the flathead engines didn't have much of a problem outrunning the 261. "There's no replacement for displacement" doesn't work if the engine can't breathe! The flatheads had some restriction in the exhaust ports, but they responded much better to porting than the Chevy.
Jerry
