RE: F-22 Raptor .61
I never even thought about a tuned pipe. I just went with the stock can.... less tuning problems that way. You won't have any ground clearance with a 12x6. I am using a 11x7, 11x8 and even trying an 11x9. I put a longer nose gear in (out of a Tiger 60 kit) and I went with 3.25 inch foam wheels to get good prop clearance. I am not sure how much weight I put in the tail but it was enough. I've got it balanced right in the middle of the cg range. You got lucky to find a GMS .61motor in stock anywhere. They have all been on backorder from the hobbyshops since late last fall. The .61 will fit the bill just fine, but with the same footprint and a whisker lighter, the .76 would have been awesome too. Beef up your firewall with a couple pieces of tristock and epoxy and you will be fine. I could only sqeeze an 8oz tank in mine and I can get about 6-7 minutes of flightime. You don't want to push the threshold and have to deadstick that bad boy!![X(] Make sure you have some reserve left for landing.
Curt