Ha, I was also watching this on eBay. I too have an A400 frame that I recently dug out of the back of my dads garage that I thought about semi restoring. Unfortunately there is so much crap welded to the frame from previous owners that it would be a real pain to un-do, hence why I started trolling eBay. Not to mention, I chopped the handlebars off 25 years ago and added some ape hangers just so I could ride it!. I really wish I didn't chop it up now that I know what it is. Did the engine and brakes come with the sale?, the listing never specified anything other than the frame. During my research, I found that they started using disc brakes in 1966 but the only image I found has a Kelsey Hayes triangle caliper not the rounded one. In fact, I haven't seen an advertisement that shows the rounded one. Also mine doesn't have the hole in the engine plate which I do believe makes yours a 71 to my knowledge, when they started using Tecumseh engines. I thought about re-popping these frames but a little beefier because the A400 is my favorite mini of all time and they aren't that easy to find in good condition anymore. Anyhow, Good luck with the build and try not to worry about getting it 100% correct as it will drive you nuts, Unless that's what you want. If it was you, I would straighten the forks, sandblast and paint the frame, re-build your Clinton, find the correct wheels and enjoy!.
Won this gem on ebay the other day... 
