OK, interesting so I took some pictures. Not the best quality but it might help.
It looks like a simple board with, besides the input jacks and the switch, a big 25W 8 ohm resistor and 2 2.2uF 250V caps. The 2 woofers get a direct tap from the input(s) (the white wire from the board), the tweeter is connected to the red one.
BTW: you might want to check the link in my signature, I think there was a guy from Sweden or Norway who did the mod to a 500 combo - if I recall correctly. Try shooting him a PM to get some help (I haven't modded my 500C).
Also, for the interested ones: there are the 2 Eminence woofers with no type nr, a Fender FBT-1 50W / 8 ohms tweeter, a brace, some padding and a better look at the 2 ports (aka: cardboard tubes, painted black on the inside).
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