I would think that 19" tires would be easier to find than 17.5's, since so many motor homes have them. Another point is that with the taller wheel you can have a shorter sidewall and still have the same overall height, that helps the handling.

'65 C-10, 65 L-60, 65 C-80, 72 C-60 & and a bunch of old Chevy cars.
Never time to do it right, always time to do it over.