My 1982 Ferrari has Bosch mechanical fuel injection, needa a fuel pump but they are easy to come by.
How about e
An epitracoidal Wankle style engine as a compressor. Relatively easier to machine with oil in the fuel to act as seals
If output voltage is the main consideration, a simple DC pm motor will work well- think Mabuchi- easy and cheap
Model dc brushless motors are 3 phase with rare earth magnets and should also worK, some are very hi power in motor use