On all my classic cars one of the first jobs I do is to fit Hall Effect electronic ignition triggering in the place of the points. I find setting points tedious, and ditto the drift in ignition timing that occurs as the points wear.
For the 504 I decided to go for the Powerspark unit, which I purchased from www.simonbbc.com. The price was great, and the shipping to Australia was incredibly quick.
After noting the distributor position (for rough initial timing before setting accurately with a timing light) and the rotor button position (to facilitate easy re-insertion of the distributor to engage with the drive tangs), I removed the distributor and removed the points.
The Powerspark unit was a doddle to fit, using common sense more than the directions on the packaging which didn't quite refer to this particular unit with the 'remote' sensor that moves with the vacuum advance. A good point compared to other units (of other brands) I have fitted to other vehicles was the inclusion of some thermal grease, which ensures a good 'heatsink' transfer of heat from the unit to the baseplate.
The job took probably 15 minutes, and the photos are below.
I recommend this unit to anyone with a 504!