[Zoomad75]

It also depends if you want it to flex and NOT wipe out the fenders when it does. What are the intended plans for said truck?

If it's pavement pounding without flexing it out the 37's might fit with a minor trim to the front fenders for turning clearance.

If you plan on actually taking it off road and letting it flex, 6" may not be enough with 37's. The 67-72 trucks have a much more forgiving wheel opening size but that's a big tire to stuff into a fender. If anything, the tires will self clearance if they are too tight. You'll hear it and probably not like what they look like.