Recovering Harris/APL source code

[apl.explorer]

There are tapes for Harris' Vulcan Operating System
located at -

http://www.bitsavers.org/bits/Harris/vulcan/

Wondering if Harris/APL source code is on any of these
tapes. The file format(s) are not decipherable by myself,
and i have tried finding descriptions of Harris file format(s)
at bitsavers.org
Anyone familiar with Harris file format(s)?
Also any additional documents which are not already located at -

http://www.bitsavers.org/pdf/harris/

Could really use some help pulling source code(s) of all
kinds out of these tapes.

William F. Gallant