They did indeed use the BW35, and not a bad box in it's time, later versions of RV8 have been fitted with ZF4HP22 and ZF4HP24 gearboxes as auto's in rangeys etc, these are awsomely strong boxes and can be converted to 2wd by using a bmw 850(etc) tail end, as mine was/is(still for sale!!), has shift kit, high stall convertor etc, this was built by John Lovegrove of ATP transmissions in bristol, at quite a few thousand £'s.
There are other box options, manual, such as MG 4 speed, or with laycock overdrive, borg warner T50, even the MOSS a real pain in the arse to fit but ace box, the BW35(auto) despite being a US design was made in the uk, where blmc had bought the rights to it, of the manuals I'd go for the manual with O/D always veiwed with suspicion but is actually a good box strength wise.
tabetha