Hi Josh.. thanks for writing.
Yes, Dub has spacers. But 1/2" is a long distance.
I had the SJ-90L on my ultrasport for a while. Flew great, and I installed without any spacers. Required sanding/relieving some of the chin block on the lower front end. A few minutes with a dremel and all was good. exhaust diverter on the end, and no issues with the wing.
Configured with a standard Dubro fuel tank in that. Nothing special. The plane has a solid front end and tends to transfer energy well. Just make sure the tank is well padded. If you want to go with a bubble tank, I think Tetra makes a 14oz that would work pretty well. Remember, you get to use ALL of the fuel in a bubble tank. Regular tank has 5%-10% unusuable fuel.... 16oz tank only has 14oz of useable fuel in it before you start sucking air.
More to your question - What I would suggest is looking here
http://www.jettengineering.com/engines/sj90-new.html
The Toni muffler extention kit gives you two things..... extra distance, and a few degrees extra outward angle. This sounds like what you are looking for.
If this suits your installation, simply order "TONI EXTENSTION SET, SJ90L" either by phone or use the on-line order form.
The system ends up being slightly longer, so your target rpm is more in the 13,800 14,000 range. Nothing lost really, tradeing rpm for torque. 11x8 and 11x9 will work great.
I hope this is helpful
Bob