Thrust definitely will play a role. If the cam moves fore or aft the gear can compensate slightly with up and down movement equal to the the cam movement. This will keep the clearance equal. BUT if the cam can move more than the gear - which a lot of guys restrict with the collar - then clearance will disappear and wear will occur. If you're using a collar to restrict the drive gear movement, the clearance should be no less than the cam thrust button clearance. Be sure to use a thrust button and get the clearance below .005. I like the roller bearing style because you can set those to zero with no worries. Nylon one's are good because it can take the friction of rubbing against the timing cover occasionally. Aluminum buttons will gall from any wear and toss flakes into your motor. To adjust button clearance I use pieces of feeler gauge behind the thrust button. Also worth noting is not all cover gaskets are the same thickness. You have to set the clearance with the gasket you're going to use in place and adjust if you ever change it.

I'm in the process of setting mine up......again. I just got the 440 source welded aluminum cover and their ball bearing thrust button. Are you doing anything extra to get oil to the button ?

I am sure that 5W20 helps. Its amazing how much that eases the workload on that gear. I know I had to adjust my idle speed back down when I went from 15/40 to 10W30 on my old engine.

i drilled and tapped the cover on my gear drive and ran a #3 oil line to it. Use a very small feed hole. .030?