Don't forget, Tony, that both torque and power vary with engine revs. If you're buying an engine for more than just driving around, you'll get a plot of torque against speed (and probably also horsepower against speed, though that can be derived).

You'll find that diesel engines have lots of torque at low revs, compared to petrol engines (which have lower peak torque but maintain it into higher revs). This is why diesels are better for towing and hill-climbing, but less good for high-speed flat racing - when the load increases, a small drop in engine revs gives the required torque increase, maintaining power output.

I don't know about other fuels, and there must be people around here who can explain this stuff better than I can. The above is just what I picked up from driving farm tractors in my teens.