Try our new info resource - "Aladdin's Cave" (Main menu)Just added a separate link to Ash's Dropbox thread (shortcut)
Here's a useful intro to dual discs:http://www.sohc4.net/?p=52
It should say you need the VERY early 750 drive plate or you need to modify the original so it drives off the two flats on the hub not the ears under the chrome plate mate. I did put up pictures on the how to i wrote.
I've welded tanks many times, I usually wash them out with paraffin to remove the petrol, then swill them out with soapy water, never had so much as a puff.I remove dents by cutting 2"-ish holes in the bottom in the tunnel, knocking the dents out using a radiused end piece of wood and hammer, they can be de-dented to nearly original needing the tiniest smear of filler before paint. The 2" hole can have a patch welded on under where no-one sees it.