Here is the question I have for @jcardona1 or @MODist @FJZilla or anyone that has done the rear wheel clearance modification on an 80.
If you had a blank slate, knowing that someday 37's would be used, how big of a wheel well would you make? Wider/taller, what would you want?
I'm pretty happy with the way I cut my rear fenders. The lip of the fender is flush with the top of the wheel wheel. And the amount I cut is the maximum you could cut without going into the door opening. I think my rear fenders will allow for a decent amount of up-travel. I would prefer to have more down travel out of the rear suspension than up-travel into the fenders to be honest. The stock 4 link doesn't allow for much movement once you 3-link the front.