Here are some pics of the various frame details I've seen on my projects.
First is a 65 front crossmember compared to a 66 frame. Some early 66 cars used the 65 style as well. Note the 65's welded on nose, while the 66 frame has it molded in:
Frame part number and date code stamped on the drivers side rail by the rear bumper:
VIN stamped on topside of the frame under the drivers door:
VIN stamped on topside of drivers side just above tailpipe hanger. Note the numbers are stamped backwards or upside down or in some sort of a strange combination!:
And another of reinforcements found on the front crossmember of my two Fremont-built 66's. My 65 GS DOES NOT have these!:
P.S. FRAME DIMENSION charts are posted in the gallery:http://65gs.com/GS_Gallery2/thumbnails.php?album=22