[With your amount of initative (chopping the head of an old mainsail,]

I didn't actually take the head off the sail. The best match up was to remove about 70 cm from the foot. This kept the sail pretty close to the old sail. The leech curve was also close. The biggest difference was the foot was alittle longer then the old, maybe 25 cm longer. I am going to change the rake and see if that changes the performance. I will keep you posted on the results.