If you're planning on running 39.5's, then you better be looking at upgrading both your Birfs and your inner axles.
Lotsa places make upgrades for both.
Smurfields (BC)
ProFields (Allpro)
Longfields (Originator of the aftermarket super tough birf)
For axles:
Allpro has some nice 4140, and 4340
PIG on the pirate board has 4140, 4340, and 300M
Lotsa options if you want to seriously beef it up.
Upgraded birfs might be enough for you, depends on wheeling style, lockers, etc, etc..
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'93 Toy XCab - 37" Boggers, FJ80 SAS, Crawler Box, etc, etc, etc....
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