You can do driver and passenger Rallye 3 harnesses properly mounted to the "package shelf" OEM shoulder belt locations. I have 2 sets in my car for HPDE weekends. There are 3 mount points in this area, and each Rallye 3 harness only requires a single tail mount point.

You can also do 2 Rallye 4 belts mounted to the lower OEM lap belt points and deal with the extreme vertical angles.

But if you're doing a cage don't waste the money on the Rallye 3 or 4, get proper 5 or 6 point belts that are 3" wide webbing and attach them to the cross bar of your cage.

The Rallye 3 & 4 are "Tuner" belts. Most people have them for looks. I think some retailers throw in a free fart can exhaust tip with a set of two.

The rest of us use the Rallye 3 & 4 for HPDE or autocross as a compromise that holds us in place much better than the OEM belts but with some inherent risk. They work well for me, and I am not at a point that I would consider a cage, seat, HANS, etc.

If you're caging the car skip the tuner belts and get a real harness setup.

 

If you just want to be held in the seat better, get a CG-Lock. Surprisingly effective, and totally safe.