Driveshaft length for a pierce mod

[mb20]

What length driveshaft do I need for a pierce mod with a quick change and a falcon tranny.

[mb20]

I have a 29.5" with a 6 inch yoke

[racin6mod]

I sponsor a local racer and I've built him 28 1/2 long driveshafts with the long yoke he has a clamped up bprc with a brinn trany.