David Billington wrote:
One point of caution with the hydraulic would be the presence of high
pressure fluid. Bath University in the UK has/had a hydraulic dyno rig
which used a valve to throttle the system and provide the load and
because of the potential danger if pressurised parts of the system
failed it was well shielded with no one being allowed within that area
during a test run.

Thanks for the warning. I've seen this happen and it's pretty scary. If
I were to take this route I'd certainly build a shield of some sort
around the valves and pipework.

Chris