Good day Bill,

I perfectly agree on shifting the 2.1L at 4000, and maybe more when needed.
I would simply not maintain 4000 for a long period of time, no more than
3500RPM for me! (Especially when the main engine parts are no longer
available. No core, no crankshaft and not connecting rod are available).
And that also to keep a reasonable fuel consumption.

I don't want to scare anyone, sorry if I did gentlemen's!

This is only my personal experience.

I have played in motorcycle engine since I was 9 years old, I think that
today I can make the difference between an engine that sounds good at high
RPM and one that doesn't, for me the 2.1L doesn't. Any pushrod engine don't
sound good at high rev, only my point of view

Best regards, Ben