I went through this when I put new tires on my Quigley. I asked a lot of questions. I wanted the right size, the right load rating, and look.
I got an email response from Alan at SMB and he said 305's would rub on my 07 Quigley conversion, so I went with the 285's. I found Ford 17x7.5 aluminum wheels off an 06 Super Duty for $100 on Craigslist. Same size as what came on the Quigley conversion, just aluminum.
Even though the front wheel wells look big on the Quigley 4x4, they quickly fill up. If your tires are too big, the initial contact point will be in a hard right turn, on the passenger side of the van, where your mudflap would attach.
I'm glad I stuck with stock sized wheels. The tires have incredible grip, the size is right since I do not want to install fender extenders.
33" maximum is your best bet. There are a lot of options. There's nothing wrong with BFG if you get an E rated tire. 285/70 17 are available in E. I got the Nitto Terra Grappler. Very happy with them.
One negative thing about whatever tire you choose: they wear out.