You can remove the butterfly assembly, including the bushings the shaft rides on and plug the hole in the front of the plenum where the shaft comes through and you don't really have to do anything with the runners. The intake air will just go through the high speed/short runner length.

Or you can rebuild a plenum better than it was built by the factory, as I've said before. Bronze-aluminum alloy bushings are what I used, but Delrin might work better, loc-tite and knurl the screws that hold the butterfly valves to the shaft and they aren't going anywhere. You're in for the cost of the bushings and three gaskets. I have a spare plenum if anybody wants me to make another one. A heluva lot cheaper than a new one from Mitsu.

Lloyd, you might be thinking of Jasper engines, in which case you are correct. I don't know of anybody who has purchased a rebuilt Mitsu engine from them where everything was perfect. JDM engines would be the way I would go if I was you. You can tell a lot without starting it with a compression tester.

John B.