Where does the harley style decompresser go? I thought about one of those but the well for the "second spark plug" (for lack of a better description) looks too deep to get your fingers in to reach the release button.
You have to machine a place for it, just like Adrian did.
The advantage of the Harley-style decompressor is that it is much smaller, and needs a much smaller amount of machining. These decompressors I refer to are aftermarket items, and are installed on various brands of engines, so they are not only Harley decompressors, but they are often seen on high compression modified Harleys. Also seen on chainsaws.
The threaded part is usually about 10mm diameter. Quite compact.
The Iron Barrel decompressor works just as well, and the concept is the same, but there are smaller options, and that is all I was pointing out.