Dave,
You can absolutely measure the bend charactoristics of your mast. I had this conversation with my sailmaker just last week. He needed the measurements as a way to judge if a current sail would work for my mast. The way that its done is by hanging 20kg off the top of the mast, supporting the mast at the base and the hounds. The other measurement is done hanging 20kg between mast base and the hounds.

Recutting an old sail is a waste of time, dont bother. The best option is to get a used sail that is close to what you need. Or get one made for you.

PM me I'll get you connected with someone who can walk you through the measurement process.

Bill