If you can't find an original bolt, I would make it. It just has to have a snout to stick into the pump tube hole and retain it. You can test fit the taper in the hole before installing. You can test after install by pulling on the pump. The length is not super critical because there has to be room for the nut to draw down. If it's too short or too long you will know because you are looking at all the surrounding area. The taper looks to be about 4 threads long and tapers about to the thread root. Just taper it to seat about half way into hole or a tad more. It's not a high tech part and can be visually tested. A LARGE bolt for such a small job because the taper tip needed to be strong.
If you find one here or Ebay, all the better.
You can see this bolt on Deve's website. Make sure she clears the crankshaft
Thanks to Deve's site.
http://devestechnet.com/Home/Project1959235
