As you've read here, the "good" PV is from Marton Mills. They don't have MacGregor as a stock tartan. Rocky of USAKilts did organize a special order last fall, but I believe that all of it went into kilts. Unless this was part of that deal, I would be very cautious about the material you describe.

There are some other sources of PV that are much lighter than the 11 ounce MM fabric, best suited to skirts, waistcoats, and such. If you can get some for $10 or $15 a yard, then I might give it a try; but I'd be prepared to have my wife wear it.

Otherwise, perhaps you can save up for 2 yards of something like the Marton Mills Jura, and make a 4-yard box pleat. I've seen photos of some gorgeous looking 4-yarders in MacGregor. [ EDIT: the MM Jura is MacGregor "hunting" modern ]