I have a 504 sitting in my garage.
My "car guy" neighbour had it sitting in his garage. He picked it up at a flea market for $100.
I know him well and he offered it to me for the same $100.
All the other neighours must have thought that I was crazy, pushing this thing down the street.
I have not had time to play with it and do not know what works and what does not.

I've wanted one of those for many years, but just never went ahead and got one. It would be a lot easier to set up the advance curve on one of those than leaning over the fender time after time changing weights and springs.

That's the understatement of the day...