If you can, measure from the mating surface on the block to the outer surface of the flywheel (side that the TC is on). After seating the converter, measure the mating surface of the transmission and then the outside bolt pad of the Torque converter.
If you compare the measurements, the Transmission mating surface to Torque converter distance should be greater than the Block mating surface to outer side of flywheel measurement.
Basically if you can attach the trans to the block and the flywheel and converter has maybe 1/8" - 3/16" (enough that the TC can spin freely) space between them, the TC should be engaged.
If not, spin the TC until it seats without much (almost none) force.