Should be on top of the frame rail, above the left rear shock mount. Application was manual, so it could be a few inches off from that location.
Sometimes it is stamped again atop the frame rail under the left door sill, but my frame did not have a stamp there. I have also heard of it being put atop the front frame rail horn, I'm not certain which side... again, my car did not have this second stamp.
Thanks for the help Wayne c , I just went out and cleaned the frame in all the places you said and still havent found anything that looks like a number. But thanks again for the help. Ive had the car for 32 years, Ill pull the frame outside and sand blast it then check to see if I can find it with it all cleaned up. Thanks Bud: hb
Found the frame vin # on my 65 coupe this weekend where Wayne C indicates it should be. Noland Adams book directed me there. I used a small soft brass wire brush to remove the grime. You need to use a small piece of mirror to see the # on top of the frame (good exercise in reading backwards). Mine was a little more toward the front of the frame section and about 1/4 to 1/2" back from edge. Letters about 1/4 inch tall. Don't grind too much, the stamp may not be too deep. Good luck.