Al, I like what you are doing with the engine but please look at the CG numbers for Jabiru carefully. I am pretty new here...this being my second post on VAF but here is what I found about the Jabiru CG....
The kit plane article has the nosewheel weight as 160 lbs.
Katie has posted a weight of 705 lbs (not painted)
The arm from Vans W&B sheet are,
Nosewheel.... 29.75"
right & left main gear.......93.25"
Assuming the weight on both gear legs is same for now(which it is not), I calculated the empty CG as 78.8" that is outside the 80.49-85.39 in.
I have compiled a list of W&B of various Rv12 from the forum and most have an empty CG of >80"
Maybe Katie can jump in and correct my figures but I have used published numbers to get to the CG and it is well forward in the Jabiru 2200
Now we look at the Jabiru3300 from Oren using the same mount as 2200 but modifying it to accommodate the 3300's addition two cylinders and the CG becomes.......
Sorry about pitching in as a newbee. Everyone here is more knowledgeable than I am and I think the UL is a great engine and will work in the 12 with the right engineering but please e careful with how numbers will play games with you!.... Please be safe!
Rahul