I like to position things like that using a bare block as a mockup device. It's a LOT easier to manipulate into position without all the weight of the crankshaft, heads, etc. hanging on it. Before you bolt or weld anything, hang the intake and distributor on it, and maybe even the cylinder heads. Finding out you're too close to the firewall to pull the distributor, or discovering the heads won't clear is a PITA!

Use a carpenter's level front to back on the top of the block to level everything before you drill the holes for the mount into the frame!
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!