A google search may be useful. You may have some luck running a starter motor backwards, or an alternator or dynamo. These are all in the right power range, and using old immersion heater elements as a load is very convenient.
I'm not too sure what you mean by a prony brake, pony brake sounds more likely.
The main difficulty with a brake is that you have to measure the restoring couple. This is not conceptually difficult, but is either expensive or time consuming.
Cheers
Greg Locock