In my experience, it may be a good running Y block, but when you tear it down you will find it is badly worn. My 312 ran good but was slap worn out. I mean the block was worn, the cam was worn both on the lobes and the journals. Found a crack in the crank, cracks in two rods, rockers and rocker shaft worn badly. With everything new it now runs real good and has for the past 10 or 15 years.