I want to build a teststand where I can test an alternator.

I plan on fabricating a test stand for the alternator.
I have a variable voltage source capable of driving enough current to
'drive' the field.
I have a dummy load to sink the output current.

What I need is a variable speed electric motor to drive the
alternator. But I am not sure how much horsepower is required to
drive a 60Amp alternator @ the equivalent of 2500 RPM at the prop.

Which brings up another question. What is the typical ratio of prop
RPM to alternator RPM? I am thinking it is 2:1.

Alternatively rather than wasting a bunch of my time - is this
something I could just buy from an alternator repair shop?

Thanks,
Nathan