the distance between the converter and flexplate does need to be measured. if the gap is too small, the converter is likely not all the way in, and will cause damage when boltiung the engine to the trans. if the gap is too wide, the converter will be pulled off the pump impeller when tightening the 3 bolts to mate the converter and flexplate (and get the nose in the crank).

you cant really measure too small a gap, as the trans should not be bolted to the engine if the converter sticks out to the bellhousing mating surface. there should be enough room to get the flexplate in there, and still not come flush with the bellhousing before putting together.

i have never actually seen one which had the wrong clearence, but have heard horror stories, so i always check. if it is more than 1/8" find the specs.