The pic of the Skybolt on the kit box shows a brace on the main gear, but it is not mentioned in the build manual nor is it depicted on the plan sheet. I included a pic of one 'Bolt with the brace. Guess it's up to the imagination on this one.

There is a piece of 3/8" balsa that is glued between the main gear between the gear that fairs-in with the bottom of the fuselage. Your 'Bolt's original builder had the option to make access holes to the gear attachment bolts to make the gear removable.

Just for idea's sake, my 1/4-scale Hostetler 'Bolt kit landing gear came with a 3/4"-wide by 1/8"-thick aluminum brace that fits beneath the main gear in an inverted 'V' and attaches to the middle of the main gear and wheel axles. The center of the brace rides on a spring to allow dampening of the gear's flex (see pic). I don't think this spring necessary for the Sig 'Bolt. A single 4-40 'J' bolt can hold the wire at the top of the 'V'. I can't see needing more than 1/8" music wire here.

EJWash