Should I try to start it

My 51 flathead 6 was last registered in 1965. Siezed. Pulled head and soaked cylinders. Broke it loose,freed up valves, changed oil and got 40 psi before i fired it.

Bar it over a little. If it turns, dump oil and fill with fresh. Pull plugs, spin it til oil pressure comes up. Clean up carb, remote fuel tank and crank it up.
There may be nothing wrong with it. Could do a compression test to be sure.

i have fired up lots of engines that have sat for extended periods. I just dont rev the snot out of them once i get them fired up.

old guy did that with a 302, on the old gas and burned a valve.
Wouldnt listen to my advice.