There are such engines around which are based on Hayabusa bike engines

LocostUSA View Topic Design Project

There are such engines around which are based on Hayabusa bike engines …
I still really like this idea. In the dead of winter, maybe.

The biggest weight of an inline engine is the crankshaft along with it’s rotational mass, people have tried this and it’s not worth it for the very small % of lowered CG you get but around 45 degrees is ok to improve room for inlet tract flow as almost all sports bike manufacturers have proven. Perhaps making this as the oil pan?
I think you have to decide why you are designing such a hybrid engine.

Otherwise, its a lot of complications and for what?
Use existing pieces in a way the factory didn’t. Motorcycle engine pieces would seem to be the easiest and lightest way to do this. From a car engine concept something like the wet sleeve block of the Alfa engine in another thread would be a way to increase capacities of an older engine thru special sleeves. There’s also the not-insignificant issue of harmonics. Just because something can be bolted together with existing parts doesn’t guarantee no issues.