I doubt such code exists, intact. The code you are asking for, 1970s or earlier, was written in FORTRAN IV (or earlier), and was highly tuned to work efficiently on one type of computer, specifically, the type of computer the developers of said software happened to use. FORTRAN IV code is in ALL_CAPS and is (nearly) flush left, nearly because columns 1 to 5 are for statement labels and column 6 is for indicating continuation lines. Code starts in column 7 and ends in column 72. Identifiers are no more than 6 characters long. And the code is chock full of gotos.
What you can find is bits and pieces of that code in the form of the Basic Linear Algebra Subpgrams (BLAS) and its follow-ons LINPACK (acronym unknown to me) and LAPACK (Linear Algebra PACKage). Development of LAPACK continues to this day. The reference LAPACK (not tuned for a specific computer) is now hosted at github. If you go to that repo, the first subdirectory you'll see is BLAS. This is a somewhat modernized version of BLAS, mostly despaghettified and indented but still gloriously in ALL_CAPS.
While LAPACK was written in the 1980s, the origins of BLAS date back to the 1960s, with much of the development effort performed by people at the Jet Propulsion Laboratory to support orbit determination. Charles Lawson, Richard Hanson, Fred Krugh, and others (most of them at JPL) worked on this software. Highly modified versions of the orbit determination software they wrote might well still exist at JPL. Slightly modified versions of the mathematical software they wrote is widely dispersed in the form of the reference BLAS, which is publicly available.