Welcome back. I used the "Will It Fit" function on the dealer's website and by inserting 1986 Pontiac Fiero SE Coupe, which is the identical body and suspension, it says it won't fit. The information that isn't given for the wheels is the offset and that may be the problem. With a custom wheel and tire, sometimes the only way to find out is to mount it onto the vehicle. In the case of the rear of the Fiero, the combo can be bolted to the hub and checked for clearance with the car on a lift since the tire and spring boss on the rear strut don't change relationship as the suspension travels up and down. The front is a little different and must be on the ground to check for up and down as well as clearance when turning left or right.
It might be a good deal on the wheels, but there are any number of other manufacturers that make wheels with that spoke pattern. Surely some of them will have the correct offset. If their calculator doesn't have the 84 listed, do as I did. The 85 GT, 86 and 87 SE and the 86 and 87 GT's all have the same suspension and body lines that would affect clearances.