Another question is can an early 63 427 block, motor mounts be drilled from the 2 holes to the more common 3 hole motor mounts of later FE blocks?
No, the cast bosses needed on the side of the the block are not present to do such properly.
Scott.
I feel the above statement is correct, as the inquiry was of an "early '63 block", but note there are some '64 FE blocks with the cast bosses for the later 3-bolt mounts (blocks are actually most often machined with a total of four bolt holes), but only drilled & tapped for the earlier two bolt configuration.
I realize this may not be directly relevant to the original inquiry, but I felt perhaps it may prove so in a future review.
Scott.