[ROWSC]

I was told by a highly respected engine builder that one plug is barely sufficient for the stock 84mm bore. He recommended dual-plug if you increase the bore (i.e., a short-stroke 3.2). I wanted short-stroke, higher compression, big cam, and carbs, and he wouldn't touch it without dual plugs.

Remember, the CIS system is pretty crude. At best, it was "close enough" and is not suited for "dialing in." I suspect it is the primary limiting factor if you are trying to find maximum efficiency. If I was doing it again, I'd go with a full-blown engine management system and EFI.

You will also need to have the lower valve covers machined. I had to have custom plug wires made. Also be prepared to buy retainers to hold the wires on the lower plugs. I used a dual-head distributor from a 964, which meant that I needed two MSU ignition units and two coils as well.