There is a simple way of getting quasi dual ignition that we used years ago on Subaru engines and also on a Corvair conversion. Given that you have faith that the distributor shaft is quite unlikely to stop turning in flight, you can mount two Mitsubishi ignition modules on a new plate ( replaces the original points plate ) built into a stock mechanical advance distributor. The setup could be arranged to set off two waste fire coil boosted sparks to an upper and lower set of plugs. Here's a pic of two Mits modules in a Corvair distributor. I cut down a Ford 6 cyl reluctor to trigger the modules. We did this earlier with a Subaru distributor which is considerably smaller than the Corvair dizzy and it could be made to fit too.