Too much endplay question.

Ive only had one engine ever lock up, (small block ford threw a rod), it had c-4 auto the car slowed down fairly fast but didnt lock the wheels up. I did have a 10 bolt (chevy) lock the rear wheels up, that was pretty scary. Its not like the car is his daily driver, it gets maybe 20 miles a month now, to the car shows and back + a little main street cruising.The car might see 500 miles before the new engine gets put in. It ran fine befor he found out about the end play problem, I dont know why that would change!?