A 1968 327 block would be a block with the same main bearings as the later 350----------so could have been a 4 bolt block------If wanting to build a hyd roller cammed engine I would suggest using on from the roller cam blocks late 80s and up----------if a one piece seal block used there is a n adapter available to use the two piece seal/oil pan---------


Mike--- altitude won't affect the ratio formulas but will affect the amount of pressure --------