At least the S40/Savage only has one of everything (x4 valves) to work on. As already said, much in the book seems to be more for the stealership's revenue than for the engine's needs, plus a forum like this has lots and lots of discussion about maintenance.
My mechanic says that he's never found head bolts that were loose, and he no longer checks their tightness during routine maintenance checks.
I suspect that the cam chain wear has a relationship to the oil used. The chain will probably wear fastest when automotive 10W-40 oil is used, and wear slowest when an oil with a very high content of antiwear compounds were blended in by the oil maker. Also, modern oils have to meet tougher wear testing with each new generation of
diesel (Cummins ISB & ASTM D5966) or
gasoline* (Sequence IV-A & Sequence VIII) engine oils.
I'd look at a Buell** instead of a Harley. Harleys just seem to be prehistoric.
*I omitted the
SM gasoline engine oils, because no one here is suggesting that anyone use one that also isn't at least rated for diesels as well.
**Or a MotoGuzzi (except the bad years) or a modern Triumph, or one of the Japanese bikes, or a really clean older BMW. Ducatis are too trick to work on and modern BMWs are really gimmicky. When I find a 650 V-Strom at a really good price I'll have a dilema. The Savage is a low cost entry level cruiser where Suzuki got a LOT of things right, and it's just lots of fun. I could use a bigger frame bike and might want to use a bike on gravel forest roads, but I'm sure having fun on my Savage.