Ty,
Simplicity is the answer to most questions.
Personally, on all my stunters, I use 1/8" pads under the engine lugs. I typically use a tank shelf with room for height adjustment.
The "Vagabond" tank vents are up to the builder. Interestingly, my 3 slobs just had the tank glued in right on the mounts and no pads, and the simple vents. The famous "slob" uses this simple system and it works. (No Stagger either)
Many people seem to think that a bipe has to have stagger. The reason for positive stagger, starting in WWI, was for pilot visibility. It moves the CG forward, requiring a longer tail moment.
Ron Pavloer had a version of the BiSlob that he called the "Stagger-Bi" with negative stagger ala the Beech stagger wing . It did not turn the same in inside and outside maneuvers. It looked nice, but he was not totally happy with it and never build another one with stagger.
Stagger is not needed for the "Vagabond" which is simply a sport airplane.
Yes, the "Vagabond" has short wings and large tail surfaces. Again, it is a sport airplane and is meant to anything you want to do. It has more span which will improve glide over it's slobby distant cousin, but remember that bipes have a lot of drag, and most will not have a long glide.
While it is possible that someone might fly stunt events with a "Vagabond", it is not intended to win the Nats. It is simply a fun airplane.