Re: tire sizes
on my 71 bronco: Axles are completely original. Dana 44 front, Ford 9" Rear. Original Limited Slip and 4.11's. Currently running 33's, but ran 35's for 3 years on highway and pounded rocks in the mountains. I have photo's of the whole front and rear 3' off the ground to prove the abuse. Never had a problem! I would be a little uneasy about runnig 39" tires with the original 28 spline axles though. I think I would even put in axle trusses. As far as the lockers go, I am not a firm believer in them. If you need lockers, the rocks are too big for a daily driver. That is just my opinion.
You obviously know where to find the best parts, FORD!
Hope the info helps