Slant six swap HELP!
he still gets overheating
Defined how? If it's just the dash gauge moves toward "H", that could be a gauge/sender issue, pretty easy to fix. If it's pinging and boilover and fountains of steam, actual signs of real overheating, when does it happen? High speed on the highway? Low/no speed stuck in traffic? Doesn't matter/always?
Assuming it's actual overheating and his radiator work was adequate and he's made sure his new thermostat isn't faulty, it could be mud/rust accumulation in the block (this takes more than just pouring in a bottle of fast flush, but doesn't require pulling the engine), could be exhaust backpressure (internally collapsed muffler, krunched pipe, manifold heat control valve stuck "on"), could be radiator fan installed the wrong way round. Could be lean fuel mixture. Could still be wrong ignition timing—the crank pulley is a 2-piece item, with the outer ring (w/timing mark) rubber-bonded to the central hub. Over the years that bond can let go, then the ring slips relative to the hub under the drive belt torque load, so the ignition timing mark is no longer accurate. Checking for this requires verifying TDC (between compression and power strokes/both valves closed) in № 1 cylinder corresponds to "0" timing indication.
