Welcome back Chris
You can either order a BJ4 directly through Jason or from either
Wings and Wheels or
DC Racing in the UK. It's slightly cheaper going direct but sometimes customs can sting you and you end up paying more, so for the lack of hassle it's usually easier to go for one of the shops mentioned.
The car is very easy to drive with full time 4wd but you might find it a bit understeery on corner entry, in which case I'd look to get a front one-way. I've used the centre one-way every time I've been to Tiverton (indoor dirt) recently as it's a lot more forgiving when the track breaks up than the one-way diff.
For the motor and speedo I'd be looking into brushless if I were you, they're legal for BRCA events now and you won't need a lathe either. Have a look at the LRP Shere competition and something like a 3* (5.5 turn I think) motor, which shouldn't be
too silly
The cells I'd buy at the moment are the GP4300's, for this year I bought GP4300's for my 2wd and IB4200's for my 4wd. Initially the IB's had a bit more punch than the GP's but their performance has dropped right off now and my GP's almost feel like new still.
Lee Martin was doing shells for people at one time (not sure if he still does), I think Chris Rowcliffe (Wings and Wheels) has done a shell or too in the past too. Both of them are fairly local to you and regulars at Tiverton