With SOA and 2" over stock springs, wouldn't you be begging for driveshaft angle problems? I've always been a little unclear on this issue, and it worries me since I had a u-joint go bad after my first wheelin trip with only a 4" lift. I really don't know, just wondering.
If the 2" over stock with SOA is too much, you can always start removing some leaves and gain more flex and lose a little height.
Well figured since I would be reangling for caster/camber for the front. I would have to make sure of the rear aswell ....... so that means shimming and welding new pads anyway. Just like my on my K5, D60F and D70HD got the same treatment.
IMO, you'll fit 38.5-42" tires great, but look awkward with a 37-smaller tire. Install the setup with the stock springs, it should only need a small shim in the rear if you later swap to the lift spring.
So what you can to keep it low. Mine rub the fenders, but 38.5 tires do fit on a "stock" SOA.
Also, lift springs, even in SOA configuration, will not be as flexy as stockers...they are hard to beat.
I'm running SOA and 2" springs with 37" tires. Yes I did have problems with the front driveline, solved it by going to a hi-angle driveline. The 37" tires look just fine and better than that work great. I've got 23" of clearance to my rocker panals and it will ramp about 950.