MaSnaka Try the FE forumn. Royce, Dave Shoe, Barry R., and other have 40-45 years with FE motors. It does not sound good, the only thing I can think of is did you or the assemblier install the head gasket the wrong way. It can go on either way, the motor will run fine but after about an hour it runs hot. Felpro gasket have arrows that point forward to install, you have to flip 1 gasket to keep the arrow forward. If you search on the FE forumn it shows you what to look for. I don't want to get this wrong for you, but you are looking for a tab on each side, I THINK.
And I just built my stroker in Sept last year. The other thing is a small crack that when the motor cools is sucks
oil into the coolant system. You could try a coolant sealer for the motor. I would first check the gaskets. Where the heads and block pressure tested before and work done? Some machinist use 100 psi and in a water tank over night. It's not 100% perfect but does catch problems. Try Gessford machine for help. Rick L. Good luck