Welcome lazy j to the Stovebolt Page. Good luck with the old truck. I agree that is a 63 or later 230 or 250 motor. I would be interested to see what was done with/about the transmission mounts. Hang in there and don't get discouraged. If you can find the serial number stamped on the flat pad behind the distributor post it here and we will see if we can help. The motor was stuck in my 50 Chevy when i got it. I used a generic penetrating oil, along with some Marvel Mystery Oil. Other people prefer Kroil, PB Blaster, WD-40 and other lubricant/penetrants. You really can't put too much in each cylinder. Try to be patient and let the oil do its work. If/when you can turn the motor over by hand and feel no resistance, with the spark plugs out (and the crankcase full of clean, new oil) turn it over with the starter for awhile before trying to actually start it. Good luck and do it safely! These old GM trucks can be alot of fun.

Professional Novice