32.5" or 36.5" sas

I'm doing a sas on a 97 gmc z71and everybody says a 78-79 ford dana 60 with the 32.5" spring pad width is the best axle to get but it's nearly impossible to find one.  Can anyone tell me why the 36.5" spring width axles would'nt be just as good?  I did a little measuring and it looks like the tires fully turned would hit the frame in the back before the springs anyway.  I want to run 38 or 40" tires with a minimum amount of lift.  Best I can tell I would nedd wheels with about 3 1/2" backspacing to clear the frame.  If anyone has experience with this or has done a simular build any info would be greatly appriciated?  

Many people flock to the earlier axle because the somewhat more-centered differential leaves more axle tube exposed on the driverside which makes it easier to weld link mounts, radius arm mounts, etc. to it. If you're using leaf springs, then there's really no reason to avoid the later axles. I've also seen where guys have trimmed the diff housing a bit on the later axles to get more access to the tube itself for welding. Because the pig is so massive, this generally doesn't present an issue if you also weld the tube itself to the pig where you trimmed it.

Another issue many like to argue over is kingpins vs. balljoints ('91down is KP, '92up is BJ). Many will swear the kingpins are stronger. Whether this is true or not I'm not sure, but I don't think I've ever seen balljoints fail due to stress on a D60 (D44s are a different story however). IMO, the only real advantage I see with kingpins is it's easier to put a hi-steer setup on it (you can do hi-steer on a BJ axle too, but it requires whole new replacement knuckles).
If you go as late as 2005 & up on a Ford D60, you'll get an axle that's already set up for coil springs, and has stock 35 spline shafts through & through (earlier 60s have 30 spline outer stubs). These are a few inches wider than earlier D60s though (around 73" IIRC). They also have a metric 8x170mm lug pattern, so you'd also want to get the 10.5" rear to match up with it.

Hope that helps.  

Thanks, I could'nt see where the 36.5" spring pad width axles would cause a problem, If anything maybe make the rig a liitle more stable.  The frame near the rear of the fenderwell seems to be the limiting factor.  I plan on moving the axle forward as much as possible w/out affecting steering (2 1/2 - 3" maybe). I will be running x-over so I will go w/ a kinpin version.  A 3 or 4-link would be nice, but I'm going w/ 52" leafs because of budget and simplicity.