I don't see a problem running both spacers for a few reasons.
1) the inner spacer has nothing to do with it, all it does is alow the use of ifs hubs on the solid axle, the spacing is for the brake rotor
So the inner spacer is irrelivant
2) These wheels / tires will be off road only, so the only time the spacers would be on the truck would be only when these tires were on
3) everyone here say's the 30 spline longfield axles are the s--t
I also have the chromo hub gears
4) As for power and gearing I don't think that will be a problem for tha small block ford or the nv4500 W/ dual yota cases,
Thats why I went with the 4:88's
5) I have a d60 rear for the truck still lookin for the front.
6) from what I have learned so far it's not so much what you run as much as how you run.
7) two words LIFETIME WARRANTY
I'm building my truck as bullet proof as possable and it's still going to break, thats all part of the fun,