i have 39.5s, had a mini front axle for a while with them. no hub studs, no cromo hub gears, stock out puts, 5.29s, reg 4 stud arms, 3" spacers and drove it very hard. only thing i every broke was the steering arm pin. i've always had an fj80 rear axle so im not sure how long the 8" R&P would hold up. i now have an 80 front axle wich still has an 8" 3rd that been holding up fine. you will def need 4.7s, i use lo lo all the time. my next upgrade is outputs, then im golden.
on another note austin(with the yellow first gen) does 90% of the stuff i do with little struggle on 37" mtrs. my opinion is really dont need 40s on a wheel base like yours
the two obstacles that really bugged me were not being able to make it up soup bowl, which you were there for, and also back door. I'm not sure if its more the wheel base, bed catching on rocks, or tire size, but i was thinking a larger tire might help. I'm starting to think I need to be happy with the 37's and look into maybe doing something else to help me out.
