This is really good to know, I really wanted to put the Saito in my FW190 and might consider it now. I think mine is still a bit heavier than yours but it’s got a lot of ballast in it with a GP88 engine. The Saito is probably heavier than the GP so may be able to remove some weight and the forward moment will increase so may be able to remove excess weight.
I don’t see a problem running the engine inverted, the FG60 ran perfectly well on the stand like that, but never tried it on a plane. I would be tempted to baffle the engine better and have it mounted in the upright position. Baffling on these things is paramount. Creating negative pressure behind the engine whether air exit is top, bottom, middle doesn’t matter..