I'd put at least a 245 on an 8.5 wide wheel. 255 or 265 would be better, unless you just for some reason like the look of narrow tires on a wide wheel. To give you some idea, Ford put 245s on the stock 8 wide Mustang wheels and 275s on a 9 wide. So, you'd want to stay somewhere in between those two numbers for an optimum fit.
Sorry, but I really can't help you on the offset. But from what I've seen most 9 wide wheels for the 94-04s use between a 24-26mm offset. So 38 sounds kind of excessive. This may mean they won't fit. Maybe someone else can be more help.