So finally after a lot of messing about with the reverse box/propshafts etc. and trying to get the car silenced to a reasonable noise level, the car was booked in for it's first Blackbird powered trackday.
This was at Wroughton Airfield, which is less than an hour from me, but was a bit of a mediocre layout. Fortunately our day went ahead, but a similar event the following day was cancelled because gypsies had taken over the airfield!
Anyway, was a very good day, chance to properly unleash the now ample power! The car was incredibly goon-able through the hairpins, much fun. Got a lot of compliments on the noise of the thing too!