I just bought a 1968 firebird. It has the 350 hood and Im trying to id the engine. I found a stamp on the right side of the engine below the head. PXN. I also found a id # to the left of the timing cover 28l141143. My heads are marked 01. I think these are junk 301 heads from the 70"s. I'm hoping that the block is not a 301.Can you use 301 heads on a 350? Any help will be greatly appreciated.