Hey there,

I have an Ironman myself I think it's a later 80s model. I don't know how much success you would have mounting larger tires on it. I know that I have 700x23s on my set up (although 700x25 in the rear, I think) and the clearances are pretty tight. You could definitely get 25s in there and maybe sneak a 28 on the rear, but I don't think you would have much luck with wider tires in front (although I have a later model with a welded full-sloping fork and I think the earlier models had wider fork corwns). Best of luck!