Marshall Bass-State B65 headphone socket

[wysiwyg73]

I'm looking at adding a headphone socket to my Marshall B65. Just wondered whether anyone has done this. If not, has anyone access to a schematic? Looks like it should be possible as it is done on the newer MB60 amp, but of course I don't expect "them" to tell me how it's done.

Oh, I've 45 years experience in electronics, so have at least a clue of how to go about this. :-)