Well, the "old Prevost" is a '95, so it's only 19 years old, and the MCI is only 39........I say "only", with tongue in cheek!
I'm attracted to the Prevost listing, because the interior needs a total overhaul, which I could do mainly by DIY(I'm handy that way).
I'm attracted to the '75 MCI, because it's done, been well cared for, and in tip top shape.
My "weighting" factors are, according to the MCI owner, there isn't room to add two bunks for my boys. The Prevost, however, needing an entirely new interior due to vandals(according to seller, they "threw trash around the inside, and it stinks"....), I would be able to make the interior however I wanted to work for us. I may have to drive it back to OK wearing a bio-hazard suit, but.......what is life, but an adventure?? (price would have to drop dramatically!)