Paul, that split construction opens up new possibilities. Not sure if the kit will accommodate the change, but it's certainly worth looking at.
I was told to shoot for 1.5 oz fuel capacity, which should allow for starting, tweaking, walking to the handle, and 16 laps with a comfortable margin. I'll be using a Fox .15 BB that I picked up oh, 20 odd years ago, never ran it until Tuesday. It seems like a strong engine.
Is that the same engine in both your pictures? One shows side exhaust, the other rear, but the head looks the same. Does the cylinder mount in different configurations?