thanks for the replies. allow me to explain:
the cables coming out of the coils and to the spark plugs are what's ruined. my more bike-knowledgable friend and i concluded we can't open the coils up to replace just the cables that run to the spark plugs. i don't remember the exact numbers, but we tested all around the coils with a voltmeter with limited success/very low numbers.
so we concluded they should just be replaced. would the set i posted from eBay work? Would any Fl703-12v5 from mid seventies 550s or 750s work? Those DYNAs look good but if i can keep it under 50 bucks on a used set i'd sure like to.
For the CB750, you can swap all the following bikes' Honda coils in, and they will fit:
CB500-4
CB550-4
CB350F
CB400F
Any other SOHC4 CB750K/F.
The only differences in the 750 coils are in the post-1975 versions, when the primary resistance dropped form 4.6 ohms to 4.3 ohms and the plug cap resistance to go with them changed from 7500 ohms to 10,000 ohms at that time. But, any of these coils will fit, and any will run with either 5,000 or 10,000 (modern) sparkplug caps.
The CB500/550 coils are electrically identical to the post-1975 CB750 coils, at 4.3 ohms primary resistance. The 350F coils are USUALLY 4.6 ohms resistance, but toward the end of them and the start of the CB400F they became 4.3 ohms, likely the same coils as were found on the 550 at the time (but with slightly different spark wire length).
The Dyna 5 ohm coils are generally a better bet than their 3 ohm coils if you are not the electrically savvy sort, as they introduce a few other issues that can catch you by surprise.
There are also some nice ones at
www.PartsNmore.com, in their CB750 section. You can use either the ones ending in -6822 or -6823, they both fit: the latter have the wires turned 90 degrees from the OEM position, but they fit (I've used some). The latter electrically match the CB500/550 and post-1975 CB750 coils, the former (-6822) match the CB750K0-K6 type more exactly.
