> has anyone done any low-cost hop ups on the original engine and gotten any usable power?

Usually the best thing is what's called a 'Stage 0' modification: make sure everything in the basic engine is working properly. Ignition and cam timing, compression, etc.
You can also play a bit with ignition timing to see if it helps.

One thing that will help any car is ducting cold air to the intake. Most of these cars suck the hot air that has already passed through the radiator. Making a duct to get 'cool' outside air to the air cleaner can give a few 'free' horsepower and will also make the engine less likely to ping. It kind of bothers me that on my 4.5 there is not an easy way of doing this.

Csaba
72 280SEL 4.5