#1
Like, have an EMG 81 in the bridge, with a SD Jazz in the neck? Is this possible?
#2
Is it possible: Yes.
Is it viable: No.

It's not worth the effort. Looking at a schematic to do that will give you a headache. And if you don't have 4 pots (2 vol, 2 tone), it gets even more hairy. It's an absolute pain in the ass to do.

Not to mention that the level differences between an SD Jazz and an EMG 81 would be laughable.
Spin 'round carousel when your horse isn't screwed in.

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#3
been asked SO many times before.

and as offworld92 above said

possible: yes
viable: no
Belief is a beautiful armour but makes for the heaviest sword.
#4
If you wanted an 81/Jazz combo then get a DiMarzio D-Activator-X bridge and PAF Pro neck. Or go for an EMG 81 bridge and 60A neck.