640 rear frame #s

The numbers are difficult to read due to corrosion, it appears as X-12-F with x serving as unknown number(s).

These numbers are also upside down above the left axle. Is upside down normal? I need to add that these numbers are raised not punched, maybe a centimeter tall.

Those are casting numbers, not serial numbers.

Very good to know Chris. Where would the Serial number be in relation to those?

Is your left axle plate bare metal? If no, paint may be filling in your numbers.

There appears to be a blank boss UNDER the axle, would it be stamped on that?

http://www.ziggysmotorworks.com/sportsc ... -frame.jpg

Check the pic, on rear frame, right side, above and to the left of the 2004, there is little box shaped casting...
what is it for? kickstart stop? the reason I ask is mine appears to be relocated slightly.

I believe that you are referring to the kick start stop. These often were welded up as a result of wear.
http://virtualindian.org/9blueprints.htm
Dusty

That is what I believed it to be...mine has been broken off, turned 180 degrees (according to broken surfaces) and welded on a half-inch outboard. I assumed that
this was done with wheels/tires/chain intact in racing environment, easier to relocate it there.

Without knowing for sure what its intended purppose was, I couldn't tell if it was a race mod or half-fast repair.

Thanks.