I may be thinking simple on a more difficult question, so bare with me, please?
Am I reading right that you have pulled plugs and find no spark? Not able to look for the other end of the plug wires to see if there is electronic or points?
Alternate plan would be to get the model, serial number, etc. for your specific engine and then look for the info on that item. I've not chased Onan enough to know how much info there is but it would also seem they should be able to tell with the right info.
This might be a place to start for your engine specifics as it seems to show a parts section:
But that may be where things get muddy!
If you can't access right now to look at it, to see which it has, does that also mean that you can't get to it to change or repair it?
Sorry for the "no help" post but trying to clear the air!