Re: 1949 L Gravely
I haven't read everyone's responses yet but I've made several straps. Heck in a pinch (such as last year when the chain broke on my starter) I simply used a strap from a cheap ratchet strap i had with me. Believe it or not- hold the hook or sometimes if its a big hook the eye of the hook (where it's connected to the strap) on the pin and make a wrap of the strap over it. It will stay on and you do 3 or so more wraps and PULL!... Well it works!
Otherwise I've used straps from old boat covers or old ratchet strap material as above. Generally nylon. I get metal grommets from Joanne's fabric shops or a good hardware store. Once I've cut the hole and hammered the metal grommet together i actually heat it up with a match (or soldering gun) to melt any frayed nylon and bond it all together.