Custom Distrubutor Cap

I do not think splicing or having 2 spark plugs on one lead will work. The plug with the least resistance will fire first and the second plug will have no energy going to it. It is not like a light bulb.
If it will help you can look at an 85 Nissan pickup motor. It had 2 plugs per cylinder with 2 coils and 8 plug wires on a 4 cylinder engine. I know your are wanting to run two 8 cylinders, but the design may answer a lot of questions.
I'm thinking, it seems there is something in the back of my mind that will work.
Keep it up.

good luck,
railroad

Measure it with a stick, mark it with chalk, cut it with a torch.

Most aircraft engines that run dual plugs also run dual magnetos. It's not just to create a bigger spark, it's more for redundancy. If one ingnition system fails, the other usually is still working, thus the plane is still flying. I don't think I've ever seen a dual plug cap in the aviation world, but then I've only been doing it for 10 years. As for running dual engines, what are you running? A few years back I read an article in either HotRod or CarCraft where a fella was running 2 buick(I think) 6ers nose to tail, and used a modified 12 cyl. distrib. (Jaguar I think) on the front engine to light off both engines. He had the coupled at the aft end of the front engine and the front of the crank on the first engine with custom sprockets and a "chain" coupler. He ran both engines as "one engine", basically made a straight 12.

Gotta ask, why not just run a distributor in each motor. It just seems like the way to do it.