I ran 4 15 x 8" rally's on my 81 G-10 van and used stock sized tires (215/75-15 & 235/75-15) and had no problems ,except once I had a 205/75-15 on the front roll off the bead while going around a rotary circle a little too fast..it might have been too skinny,or maybe the tire itself was at fault (I scrapped it because it got sidewall rubbage inside)..
I have a set of 6" rally rims too,those might be better up front than 8" but I liked the 8" ones best,they made it handle better..
It can be a chore getting stock sized tires to inflate on the 8" rims,but I managed to get around that issue..