Did you replace F6 with a 3 amp slow blow? That's the spec.

If you turn the machine on with only j2 on the rectifier board connected and all the other connectors off the boards in the backbox, does it still blow?

The couple of things I'd suspect is the MOV on the silver RF filter box in the cabinet, you took a pic of it and there seems to have been some magic smoke deposited on the cabinet. That would cause the main line fuse to blow, as would a bad RF filter. You can temporarily take this box out of the circuit to test this theory and just buy a new one if it seems to work (make sure you unplug the machine from the wall before fooling with this, there's AC voltage right there). You'd take the filter out of circuit by removing the wires and splicing them together with wire nuts (for testing only.... that's not a long term solution).

You can test the bridge rectifier for the solenoids with a multimeter, pinwiki link yopp posted can help with that. It wouldn't hurt to get a new rectifier board as you said it is 41 years old. You'd probably need to repin the connectors as well but if the machine was in a nice climate controlled environment for a long time they might be ok.

You can take the under playfield fuse out to isolate a stuck on solenoid on the playfield. It's not the coil that goes bad (usually) but one of the driver transistors.
Stuck on coil regardless of reason should blow the playfield fuse or the F4 fuse.