Axle in stock location...caster is just fine. 6" shackles BTW.
These 52"s drive just fine on the street. Never really occurred to me that the truck was any less streetable afterward.
Rear springs up front are about the most bang for your buck lift springs. They will take more work than just bolting in a 46" spring with a positive curve, unless you consider that to get any sort of decent vertical travel you will need to move the shackle eye for the correct angle. With 52"s, a lot of people end up going through that too, but the truck will still have a good ride if you don't. Actually, whatever you do, replacing that eye with an aftermarket one for a bigger bushing is a great idea, so that's all kind of moot I suppose.
I like the 52"s/56"s because I can get them off any parts truck. 4" lift springs are slightly less easy to get a hold of, but still pretty common.