[Julian_Boolean]

I think I replaced the rear axle and gear on mine with an old 1970s Scalextric F1 axle but kept the original wheels, it's now okay but it's a bit of a handful and it's difficult to get a good stage time out of it.

 

[Julian_Boolean]

All it really needs is a milder motor and a decent rear axle and wheels.

 

[Julian_Boolean]

Motor - probably a NC2 but an NC5 might be controllable - ScaleAuto do a good range of motors that are cheaper than Ninco motors. What I've done to get an NC-5 is buy a Ninco Acura off EBay for £22 and swapped the motors over, the Acura is a little underpowered with the NC5.
Rear axle is tricky because space for the gear is tight, but a Scalextric F1 axle fits
Wheels - any alloy 15x8 wheels with Ninco Porsche 911 rear tyres (20x11)

Sadly all this lot adds quite a bit of cost to the car, but the Team Slot motor is a very good motor for LMP and GT cars just a bit over powered for rally cars, this seems to be quite common with Spanish manufactured rally cars as I've just swapped the motor in my Avant Slot Manta for an NC5 and it's a lot more controllable, maybe the Spanish Slot rally stages have longer straights than UK ones.

 

[Julian_Boolean]

They are the same as most of the 934s (I've got 3 of them) but the Martini colours 934 has different rear wheels with different size tyre, and yes they are good tyres - I use them on Can Am cars and 1970s F1s, they have the added bonus of being quite cheap. The Ninco 19x10 tyres are good as well.

 

[Julian_Boolean]

That's the one with different tyres to the other 934s, I don't know the part no. or size but that one is the best handling of the 934s.

 

[Julian_Boolean]

You can usually push the crown gears along a bit with your fingers (altough I might have gorilla hands) but a Ninco pinion press can also be used to move them.