Consider a center weighted crank. It greatly reduces the stress shifted to the inner bearings because the counter weights are more in line with the forces they are offsetting. I saw the cap walk go away in a Megablock I have when I went to a center weighted crank, and the bob weight is 2432, pretty heavy. The cost difference is around 2500 for a crower, been a long time since I bought mine so it may be higher, but worth every dime for a project like yours. If you can use a 400 block, and lighten the rotating assembly as much as possible, the deal might live a decent life.