not sure what a cross ply tire is but I got 6.50X16 on early ford rims on my "T" and 7.50's on the back...
My '40 had 6.50x16 all the way around. I've got my 7.00x16 on 5" rims on the back already & will get 6.00x16 on the front eventually...
6.50's on 16x4's is easily done. 7.50's on 16x4's can also be done - did it this weekend in fact for my roadster. Those mo-fo's are big!!
have 8.20x16 on early ford rims. don't remember the exact width on em ATM. works fine. BUT, the tires are HUUUUUGE. feels like I'm driving around in a model A ford duesenburg with that size tire on it
Likewise here, depending on the application 7.50's can get to be too big looking, but will work on a 4" rim.