1987 v1500, 6" suspension kit, factory rally wheel

What is the tallest tire I can run with this setup? wanting to do a 38" superswamper tsl sx with maybe some inside rubbing and no trimming. Or will I have fender rubbing issues?

Sporting 35x14.50 thornbirds on Procomp 15x10 D-hole wheels now with a 17" footprint and am just slightly rubbing steering linkage at full right lockout, but no trimming required. was hoping to step up to a 38" and down to a 12.50" width and be ok since I'd be narrower and there wouldn't be a inch of lug hanging off each side. Let me know - thanks>

87 GMC Photos by sraey8 | Photobucket