Scored some rims, now tire question?

Well the good news is that after walking around Hershey today in the rain :sad8: , I talked some wheel guy into selling me Weld Alumastar 2.0's brand new in the boxes, for $200 for both. I already minitubbed my dart and wanted 15x10's but couldn't pass up this deal. SOOO since I was planning on putting on MT 28x13.50x15's that fit a 10" rim I need to no the absolute largest tire width I can get on an 8" rim. Jegg's mag says 28x11.50x15 fits 8" rim and I could do that but I still have room for more. So does anyone know if I could still get away with putting on the 13.50's (has 11" tread width) on these 8" rims? Will they just be puffed out and wear in the middle or will they not even mount etc.