Hi,
As I understand, the 10% rule only applies to National and International classes. However hinge lines may fall anywhere and airofoil sections maybe changed. I also understand that the Glens Caps are fairly close to scale and well within the 10% rule...well the 30% is, I assume the 68" one is too. As for size theres nothing stopping you flying a 68" cap in IMAC and doing realy well.
Regards
Rich