best place to find used 100hp engine

I'm looking for a ready to run (all accessories) type 1 used engine for use in testing an aircraft propeller. I would like to get 100hp at around 3500 rpm (I'll have a gear reduction so my prop speed will be lower).

I don't need a rebuilt engine as this will just be run on a test stand. I'm not super familiar with all the different models of engines, etc and what years they came on vehicles.

What specific model of engine should I look for to get this power? Where should I look for it?

I'm familiar with

I would like to keep my cost down under $750 for a complete running engine.

Also, am I going to have problems keeping it cool running it at this RPM for long periods of time (days) and how best to do it?

Thanks folks.

Joe