jfink,
I think that the pre-cut masks would be a great idea, but the possibility of difficulty of placing them and variances in framework dimensional accuracy from kit to kit would appear to be harder than it needs to be.
Honestly, the easiest and cheapest way to get fantastic results the first time, every time is to mask with Bare Metal Foil. It conforms to any curvature (or just use a couple of pieces), is thinner than any other type of tape, cuts and trims very easily to allow razor sharp edges.
Plus, you can use it for your car models or for bare metal finishes for aircraft.
If you haven't tried it, get some - you'll love it.
Cheers'
LeeTree