It's not just a matter of price. Best & Lloyd made various pumps with different pumping capacities to suit small or large engines. For example, the Best & Lloyd fitted to the vintage Matchless 250cc bikes are smaller than those fitted to their 500cc singles and 1000cc vee-twins of the same period. The capacity of the small pump is up to 200cc per hour, the large pump is up 500cc per hour. Both pumps are adjustable but usually the large pump does not give the necessary accuracy when the flow is reduced to suit the smaller capacity engines hence Best & Lloyd made the smaller pump.
Do you want to be original and fit the right size pump or fit the larger but cheaper model then alter your engine to hopefully cope with the extra oil? Some will go one way, some the other. At least we now have a choice.
Cheers,
