If that XR-6 holds together it’s a done deal! Yeah Baby!!!
If your engine can turn and hold 8000-8500 Rpm’s I would run with a 28 pitch…
A 28 pitch w/1.78 gears, @8000 Rpm’s = 112 Mph…
A 28 pitch w/1.78 gears, @8500 Rpm’s = 119 Mph…
If your going to run 7500 Rpm’s a 30 pitch = 112-113 Mph…
Running 8000 Rpm’s a 30 pitch = 120 Mph…
Just trying to help man… I am excited for you and us Allison Owners!