If you're going with 33" tires, they will fit without the spring-over. That's the largest diameter tire that will do so with the M101 CDN stock configuration.
That will not solve the fender width issue, though. If your state is one that requires covering the tire with the fender, then you'll need to make wider fenders for just about any tire that wider than the skinny stock tires.
BTW, if those tires are the one's the trailer came with, you'd be wise to check the date code on the tires. They may have been changed out in military service, but if not, then they're pushing 20 years old. Dry rot, etc make them really iffy from what I've heard.
Congrats on your purchase. These are great little trailers that will hold their value.
1997 FZJ80 The Sacred Cow 152k, 255/85 R16 BFG KM2 on 16x8 Toyota Steels Rims, ARB w/ XRC12, dual batteries/Hellroaring isolator w/ Blue Sea battery switch feeding winch and dual inverters, CDL switch w/ 7-pin mod, cupholders!, 8-ton pintle hitch w/ GI chain plate, blue-PHH, working power antenna, FSM, camper conversion
M101 CDN Tagalong to the boonies, 255/85 BFG KM2 on 16x8 Alloys, w/ custom extra wide fenders, fresh OD paint, bungied tarp and bows