Which tartan for MacClive?

[Nathan]

I guess I never did make it clear that the Great-grandmother is my father's grandmother if that makes any difference.

I don't think it makes a difference. If it were me, I'd just wear the tartan associated with my surname, given that it comes from Scotland, even if its history in Scotland is possibly comparatively recent. As Peter points out, there is certainly a social taboo against mixing the symbols of more than one clan as sometimes the two clans were not allies but it's your clothing and your family and you ought to choose whichever association you feel closer to.

It's only my opinion. You have a surname that starts with Mac. Many who wear kilts and tie it back to a distant ancestors aren't carrying names that evoke a Gaelic heritage so immediately. If your surname was Kowalski and your nearest Scottish Ancestor was a MacCorquodale, I'd say go for it but given the fact that you have a provenance in your family that the ancestors that gave you your name were MacClives, I'd either honour their district or invent a tartan. The second option is admittedly more expensive. As Peter points out, you can proudly wear MacCorquodale if you like since that is your closest Highland connection. It's your decision to make.