Rick122S;121693 wroteHow is having a head mounted distributor or external oil pump a disadvantage of the B234 if its stock fitment on the motor, is reliable and doesn't need changing?
I know nothing about sprint car rules, but they may require a points-based ignition system, so I may be completely wrong about that.
The oil pump issue
is a reliability problem - the B234 oil pumps were made only for the four-year run of B204 and B234 and they used to break oil pump pulley bolts and take the timing belt to oblivion with it when they did. On top of that, the oil pump pulleys were known to crack. Even in Mum and Dad road car use. Again, the pulley was a uniquely B204/B234 part, and they are NLA from Mother Volvo. Nobody in the aftermarket AFAIK makes oil pump pulleys for them, either. These are not good omens for a competition engine that's going to spend much of its running life revving its mammories off.
OTOH the B230 oil pump has been around forever; quality replacement pumps are easily obtainable from Mother Volvo and Melling, and when the little retainer ring is used on the pump drive, they very rarely fail in competition use.