Same here. Located the motor so all components played nice with each other.
Leveled the motor side to side.
Measured where the crank was in relation to centerline at the front and at the trans tailshaft at the rear. Make it the same, not crooked in the chassis.
Used the carb pad to tilt the motor down in the rear. You can also check for roughly 3-5 degrees at the oil pan rail.

Measure 3 times, make sure nothing is moving then build mounts. Also allow for a small amount of sag in the rubber mounts. You don't want something to 'just clear' underneath without the weight of the engine/trans supported off the mounts.