Crank Thrusting Foreward Issues

The crank bolt has a bit to do with the balancer working properly - but the balancer has nothing to do with excessive endplay. Yes, main caps move - but they are not supposed to. If you used stock caps and stock main bolts they are probably moving. If the engine is getting detonation, they will move more. You can see the movement at the cap parting lines and the bearings themselves. You have a lower end issue. Best tear it down and check it all out. It's a lot cheaper before it fails...