TimJ

Frames from the 70's designed around 27" wheels often have plenty of clearance for wide-ish 700c. I've rebuilt a couple recently and with 1 1/4" 27" tires on them there's maybe 15-20mm on either side, I think a 32 would fit fine with enough clearance. And those bikeboom bikes all came with centerpull brakes which work pretty well and give a good amount of clearance too. Those 70s 10-speed frames are tough and versatile and can be converted to a lot of purposes.

I've considered doing this myself but haven't just because the wheels are a sticky issue. I feel comfortable riding 30-year-old wheels on the street, but I don't think I'd want to put knobbies on them and do any aggressive stuff off-road. And the spacing on them is usually 126 so it just complicates upgrading a little bit. If your centurion has 700c wheels I'll bet it's 126mm spaced. If you found like an old nishiki complete for cheap you could potentially just combine the two to make a cheap cross bike.

What's better though, and still cheap to do, is converting a hybrid from the 90's. Someone made a thread here about their specialized crossroads they converted and it turned out cool. You can sometimes find those 700c wheeled hybrids for pretty cheap. I have 2 now. I paid a little too much for them ($50 each) but they're both chromo steel frames with semi-relaxed geometry, lots of tire clearance and cantilever brakes. I figure once I'm done with one I'll have maybe $200- $250 total into it.