A few random thoughts. I see no reason the end play of the ramp component cannot be checked with the chain on. Using a dial gauge.

Also never having a 603 type pump apart but looking at a picture. Could not the bearing shaft be pressed out and an open bearing just replaced with a caged or sealed one? Should be far less than 15.00 for a decent one at a bearing supply place. The shaft diameter is critical but a small outside diameter diferance not so much if this turns out to be a real oddball size. I doubt it would though.

Just from the posted picture unless I am missing something the bearing change looks doable. If this is true the choice of a replacement bearing must be considered.

Also does lifespan of the pump depend partially on vaccum leaks? The pump would experience more work and wear possibly with vacuum leaks. I
posted this last item a long time ago as a possible good reason to get rid of vacuum leaks besides the operational considerations of having them.

There must be some reason people have not been changing the bearing out. Perhaps just because after failure it is not possible usually and the mind is preoccupied with the damage.

Pre emtive strikes are another thing though. I could see people missing that. The swiveling yoke could be rebushed if there is enough meat to do it as well. I suspect it has no bushings but again have not looked at them. If bushed again a bearing supply house should have suitable replacements if required. In otherwords is an at home pre emptive partial rebuild of the parts that may cause serious issues possible? The 603 pump is far from cheap new.