Your fit technique sounds fine but you might be screwing in the bolts a bit too snug before using the jack and 2x4. Leaving it jacked up for half an hour while you have a coffee might be a good idea, That gives it time to slide and the seals time to compress. Torque down all bolts and don't remove any to fit the pipes and hoses. If a bracket uses one of the bolts fit it correctly at the same time. Removing one bolt might allow the pump to move again. I've not fitted a 164 pump, only B18 ones. Yes, I have fitted seals that were too long and had them collapse, that's easy to do. I've also fitted a pump that seemed OK but leaked from the seal after the first long trip. Cured that by loosening the bolts and then using the jack and 4x2 again. I just use a smear of grease on both sides of the gasket, applied with a finger. That holds the gasket in place initially and gives enough slide to position the pump.