Actually, done right and if in good shape, I don't see a real problem here. As long as no large loads were to be carried, the truck's brakes should have been fine for regular driving. A '51 Olds was 135 HP, a far cry from the 400-600 HP engines people are commonly using now. Admittedly, I'm not an expert on 1935 Internationals, but from what I do know, you would probably be looking at 2-300 lbs. weight increase and about 50 more HP. Done prudently, I'd drive that all day as long as it cooled well.
People on this very forum swear up and down that done right, Ford mechanical brakes are as good as the early hydraulics. I would expect International brakes to be as good or better than the Fords, being purposely made for trucks rather than cars.