Ken and others...
I'll admit that between other 'things', I've been working on an electronic ignition trigger kit. No details at this time other than it will be:
1) inexpensive
2) reliable
3) adjustable
4) using Captain Kirk's Points-Saver as the final drive for the coil.
RE "180-degree firing"- This is referred to as 'wasted spark', and is extremely common on twin-cylinder 4-stroke engines, using a double-ended coil- one end to each plug.
The disadvantage to wasted-spark...
1) plug runs hotter, and can become source of preignition
2) coil operating frequency is double that of normal configuration. Where inductive reactance is a function of frequency, the operational impedance rises substantially, throwing lots of available spark energy into the ashcan... the solution is to replace the coil with a less-efficient (and more expensive, in terms of kit-cost) coil.
3) The wasted-spark event needs to be carefully located so that the intake valve isn't open when the spark goes off. This, in effect, limits the range of timing adjustment. With lots of valve overlap, or hammer-fisted timing adjustment, you can touch off the plug while the intake valve is open. Flatheads tend to not burn the charge completely, and some of the leftover charge will go off in the wasted event, causing the fire to flash up the intake(whoof!), and you'll be picking pieces of your carbeurator out of the garage wall.
It's tricky, and the original Kohler electronic stuff was unreliable. Wish they'd revisit it, but they haven't.
As for the different sensing techniques- Hall effects seem to work nicely (PerTronix uses 'em, and most automotive crank-position sensors are), but they don't like heat, high-frequency vibration, shock, extreme current, or electromagnetic spikes... all common on a K-motor. Unfortunately, they're also costly and hard-to-mount in an 'easy' package, and when subjected to just-the-right electrical conditions, will 'stick' in one state... which is why they're such a PITA in automotive applications...
IR/LED shuttles (like the Mallory UniLite) work nice, but don't like dust, dirt, oil, heat, or electrical surges. They are a tad cheaper, which is a good thing, because they're less expensive to replace when contaminated or fried.
Both hall-effect and optical sensors have speed limitations- they can only switch states so-fast, so when selecting one, the switching-speed of the triggering-technique must be calculated first, so 'ya don't cause it to be an accidental rev-limiter.
All this is the reason why, if you remove the ignition trigger system of most cars today, you'll find an induction coil and reluctor. They don't mind dirt, moisture, vibration, heat, oil, shock, or electrical surges. They're inexpensive, fast, and very predictable... just requires a bit more interface circuitry.