250 6 cyl engine problems - need some input

[ScottH]

Recently bought a 72 C10 with a 250 3 speed drive line. When I bought it the exhaust leaked really bad, thought the doughnut was shot along with the tailpipe. Found out the exhaust manifold was badly cracked, so replaced it.

Got it started after replacing the exhaust manifold and it ran really crappy.
Rebuilt the carb and still running lousy. Checked timing and it would only run half way decent way advanced. Decided to do a compression test and found cylinders 5 & 6 very low (90 & 60). The oil shows no sign of water in it, except that it is over the full mark.

I'm thinking a blown head gasket. I just dont want to put a lot of work into it only to find out the head or block has problems. As it is I would have to replace the carb and still not sure about the timing issue (checked TDC was correct, plug wires correct, etc.).

Any ideas or suggestions what to do next?

Thanks
Scott