The top of the block had darn well better be parallel to the crankshaft! The first thing I do to a race engine is align bore the main bearings, then I deck the block, using the mains as a reference. Just put a magnetic angle gauge on top of the bare block, with the bubble set at 3 degrees, and do whatever shimming of mounts is necessary to level the bubble.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!