Leigh i have two T5 gearboxes spare, one was mated to the cosworth the other was mated to a standard speed six i dont know if either will fit your RV8?
I have a T5 with TVR / Rv8 bellhousing so just need the bit to connect to the propshaft. and some kind of gear stick, I weld something up so its in the right place, just need the fitting.