To install,

put this version of PCL in cmucl's source directory, and name it pcl.
rename the cmucl file  tools/pclcom.lisp  to  tools/pclcom.lisp.original
link the file  impl/cmu/pclcom.lisp  to  cmucl/tools/pclcom.lisp
link the file  impl/cmu/pclload.lisp  to  pclload.lisp

For example, 

cd cmucl17f
mv pcl pcl.original
<<install this PCL in the pcl directory>>
cd tools
mv pclcom.lisp pclcom.lisp.original
ln -s ../pcl/impl/cmu/pclcom.lisp pclcom.lisp
cd ../pcl
ln -s impl/cmu/pclload.lisp pclload.lisp
