I have a RV8 in my cobra..
3.5 sightly modded but nothing like that though... couldn't afford to do that....
They are a very nice and forgiving engine.
mine was as smooth as anything when i first tried it prior to stripping.
Had it resting on a piece of wood with one tie down strap on it and it didn't move, or even shake!!
When i opened it up the crank was toast, and there were no big end or cam shaft bearings to speak of!!
Not as impressive as yours but I like it....

If things were meant to be easy, then I will soon complicate them....
Please note...
Anything I say is only from my personal experience and knowledge..
I don't assume to know everything, and know there is a lot I don't know..
But then I could be talking bollox.. O:-)