The main measurement would be the overall measurement in what would be the hanging portion of the kilt. The flaring of the pleats CAN be made to adjust for the difference, but it would take some planning.
Let me explain why (unless I am wrong and bull headed in this matter):
The 60 inch measurement is only valid for legs on plants, as the inner thigh portions are not relevant for a kilt, while the gap between the mid front and mid rear thighs is VERY relevant for a kilt, as it would also be affected by any bowleggedness.
I figure the relavant measurement would be 15 inches per leg, plus the front and rear apron and pleat gaps. The total may be 60 inches still, but it may not. Also, at least for me, I would also like to know the relative proportion of that measurement, as it may affect the flaring of the pleats to compensate for size difference. If the hip/butt measurement is 55 and the mid thigh measurement is 60, it would CERTAINLY affect the hang of the pleats.

The pre-milled kilts and patterned ones would not have such compensation built in. As for the USA Kilts, I'm sure Rocky could make it work, but I'll have to let him speak for himself.

The above is my first impulse answer, I'll have to do some thinking and figuring to see if I want to adjust it any.