Well, well,
Looks like another very early bird!
I'd be interested in some more photos, even if the machine is in a state of dismemberment.
One thing I am curious about is the decal. It has a red background? Mine and gml's are green. Does it have the gear motif style decal on the front?
Take heart in the fact that your machine is still in better condition than my own example when I got it!

We can certainly help out with a seat and the piece of missing tinwear. The seat will be ex a tractor model. They are very similar with just a slight difference in moulding underneath which no one will notice anyway. The tinwear is unique to these very early machines but fortunately is very simple to fold up. I need to fold one for mine as the original is hopelessly rusted. It'll be just as easy to make two as to make one. Let me know when you get close to needing it.
Throttle, I know gml was looking for one a few weeks back and found one somewhere. They appear to be literally a Victa one with the cable cut to length.
Can't help with the tank. I'll keep an eye out for you.
On the subject of paint, I went to the trouble of getting an accurate match in 2k but also picked up a can of killrust red rattler for little bits and pieces and it is an incredibly good match.
Cheers,