John - I think the price difference is due to the Schroth belts being DOT approved where Sparco is not. I've been looking at a lot of options, actually too many. I don't have a cage yet so "correct" mounting options are limited. I'm leaning to the Schroth even though the price is higher because they appear to have a better buckle for adjusting and the ASM system to prevent submarining, not because of DOT. Also the offer a more tuning belt shoulder harness mount options than Sparco.
In my car with the older Recaro seats I can run the shoulder harness through the head rests since the mount rods are space 9.5" apart and Schroth's stated minimum is 4.5". The problem is a suitable rear anchor point. Using string and an angle finder the line from the headrest to rear seat belt mounts is 48-50* from level ground. Stated minimum is 45* but that is far from desirable if you look at racing harness regulations which are roughly 10* +/- from the shoulder level. The other issue with the rear belt mounts is they don't allow a straight line from the mount to the seat back due to interfence from the bottom of the seat back. To get straight-line pull the seat back would need to be slotted.
Using a single tail strap off the harness and utilizing the factoring shoulder belt mount isn't a good angle in the Camaro either IMO. Using the rear passenger shoulder mount location on the package tray next to the speaker opening appears very weak (even if a backing plate is used) for a single mount if subjected to a major frontal impact. That's why I'm leaning towards the Schroth Rallye 4 and using two reinforced mount points in the package tray. The rear seat back is about 1.25-1.5" higher than the package shelf which means ideally the mount surface should be at least 1" higher than the package shelf. The quick way might be bolt or weld in a piece of 1x2 tubing behind the seat back and anchor to that.
All these factors make a Tiger Cage tempting.......with the exception of cost in my current situation!
Package tray
The seat centerline is very close to the center of the speaker opening. The factory rear shoulder belt mount is at 7:30 1" from the speaker opening.
Rallye 4
Rallye 3 for comparison: