There is very little difference between a generator and a motor in real life. In fact, it is easier to get electricity from a motor than it is to get from an alternator. I feel that a player should be able to take a motor, add some amplifier circuits, and perhaps add some more wire to represent replacing the permanent magnet with a second winding.
it would go something along the lines of
small motor + missing stuff = motorbike alternator
motor + missing stuff = car alternator
motor + missing stuff = truck alternator
large motor + less stuff* = 7500w generator
*(generators would use the same amount of wire as the motor since they use permanent magnets unlike alternators.)
In order for this to work, the weights and disassembly results of alternators would have to jibe with their motor counterpart.