Ok, try this but you must obey all common sense safety first principles and rules....hot oil.
Get a small sauce pan and camping stove. Small Sauce pan with a lid.
Outside, in no rain or snow type weather, set up stove. Place sauce pan on stove. Thread copper wire thru advancer centre hole to make easy to use handle. Place advancer unit in sauce pan after having checked it for no hot oil damageable parts, drive side down. Pour in enough engine oil ( even used ) oil to cover most of the unit. Heat oil until just before it starts to show the hint of smoking. Remove saucepan from heat.
You may see oil rise between advancer base and moving cam, capiliiry action, along with rust...
Allow to cool down.
Does the cam now rotate, even slightly, on the base unit ?
If yes, patience patience patience.
If no, repeat hot oil.
Rotates this time ?
No.
Third try....
No joy...
Set up on firm bench, wood blocks either side of advancer base, cam downwards, with enough clearance, so that a "gravity hammer" can be used.
Place advancer in oil, cam end down, with sufficient oil to heat the cam. Heat oil.
Turn off heat, gloved hand, remove the advancer from the hot oil and place the advancer base only in cold water, to cool the base a bit, use gravity hammer/momentum to hopefully cause the cam to come off the shaft it turns on.
The cold water should be at least 10 foot away from the hot oil. DO NOT allow water or anything else anywhere near the hot oil.
You could of course, set up the advancer so in hot oil, the cam drops off the shaft due to gravity.
Naturally, no pets, kids or d#£&@55es anywhere near that hot oil.
Before you do any of this, make your self fully aware of all the risks of using heat, hot oil etc. and only do this technique OUTSIDE !!!!
Research " chip pan fires", this is important.
I recon with a good initial heating the parts will turn at least.
Your picture shows no sign of "riveting".....
The hot oil technique works on all sorts of problems, I have to use it from time to time, this being one of them.
Stand by......
Dd23🤓