Air craft auto
You can most often get one lent to you at your local aircraft section at the auto supply near you. Just tell them you are putting on a converter and need to hold it while putting the bolts in. But if you want to spend a lot just to have one ask Snap-On to sell you a Fly-wheel holding tool. The last one I got off the truck was about $70, but that was a long time ago. The tool is not hard to make but the factory ones are nice for a lot of things.
Yours as always, R.E.A. III #80888