It sounds like you're practicing everything you can with the planes that you have available to fly currently. One of the reasons that the Skybolt is so popular is that it flies more like a sport/pattern plane than a traditional scale biplane. Getting very, very comfortable with your Sky Raider Mach II sounds like it should be good preparation for your Skybolt maiden.

From the problem you describe trying to fly knife edge with the Mach II, it sounds like it might be underpowered or noseheavy or both. The Mach II doesn't have much rudder surface to fly on, but I'm wondering if it wouldn't fly a knife edge better with a ball-bearing .46 on the nose and the CG a little more in between the two settings you've had it at so far. You sound pretty comfortable with building, repairing, and modifying your planes; you could even consider slightly extending the rudder on the Sky Raider Mach II to improve the tail authority for wing overs and knife edge flight.

Other than those considerations, you might want to practice greasing in your landings with two or three clicks of throttle above idle and try to get used to coming in a little "hotter" than you normally would with a trainer or sport plane. The Skybolt will need to be landed a little faster than the two planes you're currently flying, and should slow down more quickly once its on the ground and the throttle is cut.

Those are my thoughts for now, hopefully you'll get some additional suggestions here.