929 or 954 engines will not swap in
Not without serious alterations anyway.
The swingarms of those two bikes bolt to the rear of the engines. That large protrusion will interfere with the 919's backbone-style frame.
The 900rr engine mounts similarly to the 919 but there'd be no significant power gain and therefore no point.
I'm working on something else and hopefully will have something to show for it in another week or two.