Here's the skinny....
The engine does not have to be level, nor does it have to be perfectly inline with the pinion....

The carb should be level.

The angle that the engine is installed at (let's say 3 degree's) needs to be repeated at the differential (with an * here)
So, if the engine is tilted 3 degrees up, the pinion needs that same amount up (3 degree's). (Here's the *....drag racers will put the pinion down a few degree's to account for spring wrap upon accelleration, whick will bring it to three degrees under full throttle. Most street cars shouldn't do this as you spend some time decelerating too, and this could cause a vibration in the drivetrain by having an excessive angle on the pinion.

Whatever angle you have at the trans yoke should zero itself out at the pinion.

The engine can be a tad offset to one side also. Some oem's did this to account for the fact the pinion is off to one side of the diff, but then again some diff's are offset to put the pinion in the middle. Sometimes the engine is set to the side for weight balance, but most of the time it is to clear something like the steering gear or brake booster.

Don't be skeered. Set it in there and start measuring things up.
Just keep good notes and measure it thrice...
Jeff (BTDT)

Originally posted by oldways
im trying yo fit the engine in and have space fore the steering exhasts and etc.... how level does the engine have to be on the horizontal plane front to back

my engine block # is 3970010 this # is on the engine on the drivers side above the bell house what is it and what year.

i am also confused about another aspect the lower pully mounts onto the harmonic balancer and that mounts onto the crank on my engine it looks like there is a bolt missing right there in the centre. the shop i got this from says no!! man i looked in there and there is thread and all please help....