Re: the sail size of your Macwester genoa, the foot of the sail is 18′ 6″.
The luff you will have to measure for yourself because foils are made individually. The way to this is get a long tape measure or a piece of string, tie it to the uphaul, haul it up and then mark the bottom. Take the measurement if you have used a tape, or measure the piece of string/cord. The sailmakers will work the leech out themselves.
Unfortunately, we have all the sail measurements for your type of Mac, but genoa sail measurements are not given on the documents in our archives.