I just got off the phone with Brison Engines and they have a NEW 4.8 (80cc approx) twin that is going to be in stock in about two months that will be 10 7/8" wide from plug cap to plug cap with standard length plugs and 9 3/4" wide from cap to cap with special shorter plugs. According to Brison you also gain about 100 RPM with the shorter plugs. The new engine is also going to be 1/2 pound lighter than their previous version of the 4.8.

They also have a new 6.4 twin (100cc approx) that will be in stock in about two weeks. The 6.4 measures 12 1/2" wide with long plugs and 10 1/2" with short plugs. I told them about the Weeks Solution to include the weight and they suggested the 6.4 if I want unlimited vertical. I am going to take a look at the cowl and see if the 6.4 will work, I think it might. The 6.4 sells for $995.00 and the mufflers are about another $100.00. Both of these engines are the most narrow twins I have seen yet.