[Mr70]

Yes,sometimes the Body's VIN# will be stamped on the frame,but not always.It will be a shortened VIN#,called a CON (Confidential) VIN.
Example-if Cars full VIN# is 136379K123456,look for 19K123456 stamped on the frame rails were I described earlier.
The other numbers you stated are the Frame Part number etc.
Breaks down as:
*#3943331=is a 1969 Chevelle 2 dr. frame.
*S= is A.O Smith Manufacturer
*8=August
*6=day
*9=year
1-Shift
XK=was used as a 1969 Chevelle Frame suffix code.