Congratulations on a great find, Ron!   The cord is the only major thing that isn't original.   The one you have is from a 60's era Sanitronic.  The orginal cord would have been shorter, grey, and the machine end had a round plug rather than flat.  Finding a cord and a grey bumper is going to be tough but after finding a machine with the original bag, luck appears to be on your side!  I can't see in the pic but is the little tab on the belt lifter broken and that's why you're looking for a different one?  Though rare again, they do show up sometimes on ebay and elsewhere.  I would gently vacuum out the inside of the bag and leave it as-is.  I learned the hard way once that even rinsing can cause the pattern to lift off the fabric.  If you want to use the 512 I would get a different bag and preserve the original one.  The plain black bag available from Kirby now would look fine on the machine and I've thought about the same thing;  taking a plain bag and silk-screening the design on it.  Good luck restoring this great piece of Kirby history!