3.9 Odd fire vs Even Fire

Haven't done so, but perhaps you could add a Pertronix Ignitor for the slant-six to your V-8 points distributor. The Ignitor has its own "reluctor" and the distributor shafts might be the same between slant and small-block or close enough to adapt w/ a bushing. One reason I suspect this might work is that I have had Crane Cams XR700 kits that I recall came w/ optical wheels for 6 or 8 cyl, which suggest the distributor plate pickup mounts are the same. You can't get there w/ the XR700 because the plastic optical wheel fits over the rotor cam, so a 6 cyl won't fit a V-8 cam.

What many do for Magnum swaps is use the flex-plate pickup. When used w/ an older 904 tranny, you just cut a slot in the bell-housing top and use the Magnum pickup w/ holder that comes off 2 bolts (search posts w/ photos). Of course, then you must use the Magnum PCM for spark, but that is easy if also using MPFI (I would).

Another approach is to fit a Ford EDIS ignition. That requires a 36-1 trigger wheel on the crank and VR pickup. I put one on my 273 engine (post w/ photos) so "should work", dep on your pulleys. I haven't run it yet. But that requires a spark controller (Megasquirt, etc).