Look at primtype.lisp and objdef.lisp (and early-objdef.lisp) for more
up-to-date definitions of various tags. (For example, the simple
string tag has changed since object.tex was written.)

The string format has changed. According to "object.tex", string length is
stored in the 24 bits of the string header. Instead, those 24 bits
are set to zero, and string length is encoded in the same way as the
other specialized simple-array counts, as a fixnum following the 
header.

The number of slots for objects has changed since object.tex was
written. The only reliable source for current slot definitions seems
to be the primitive object data maintained by the compiler itself. See
primtype.lisp and objdef.lisp, or look at the genesis code which reads
this data to generate the various slot offsets in the C header file.

The meaning of the function-self slot has changed in the X86 port:
it points directly to the code to be executed.

Nothing about FDEFN objects seems to be documented. FDEFN objects
replace the simple SYMBOL-FUNCTION slot with a much more complicated
mechanism, which I [WHN] dislike and would like to get rid of, but
haven't [yet?].