The dual inline 4 CDi's should work. That engine design is basically an odd fire twin 4, has 4 rod journals with 90 degree crank angle. Jag refereed to their V12 as a twin 6. it also had shared rod journals, same crank angle as the straight six. The firing order should be easy enough to figure out... keep in mind these CDi's are referenced to crank rpm in the program coding, referencing off the cam will change the ign advance timing... Set it up on the flywheel, one ign system setup to trigger on the south pole magnets, and the other setup to trigger on the north pole magnets, that way they'll ignore each others trigger, or stagger the magnets and hall sensors.

I think one of the reasons it won't idle very well is, there is a lot of internal resistance, especially on the piston rings, Ol jonnyQ nearly broke the first one putting in the ring groove, made a horrible crapping sound as he pushed the piston into the cylinders, I suspect those rings will take forever to bed in. Possibly a bit more mass on the flywheel will help the idle