What I do not like about spacers is that more often than not a simple spacer will not be either hub centric or wheel centric.
Ideally one wants both inner & outer to be centric to what the spacer is being used on.
The hubs design is to take the vertical shock of bumps in the road, the wheel lugs are there to hold the wheel to the hub.
I have `99 GTP rims on my `94 Cutlass Supreme, you`ll need at least 1/4 clearance on the front to clear the calipers. I bought a pair off the shelf at Autozone that work great and I didnt need to get longer studs or replace the lugnuts at all. Even transferred the Oldsmobile center cap over to the Pontiac wheels.