Heres a little how to for making a BP 2spd or all steel one.
Parts needed:
2spd
HPI 77058 (18t)
HPI 109046 (38t)
HPI 109448 (Need 2 of the black plastic spacers)
HPI 77064 (24t) ***only available from the UK***
Hot Racing Steel or Titanium 44t first gear
HPI 86362 (One way bearing for 1st...