Hi Hugo,
I was working at North American Rockwell (later Rockwell International) when we became the first second-source to MOS Technology on the 6502 family of parts. The R6520 was NMOS, and later the R65C21 was CMOS N-well silicon gate technology which was compatible with the NMOS parts (not sure of total drive capability).
We had a close relationship with Commodore who provided the schematics for the PET 2001-8 computer when they came out as Rockwell provided PET's at cost to any engineer in their Electronics division that wanted one for home in order that they might get familiar with the 6502 line. That is how I got my first PET in 1978. They did the same thing when Rockwell produced the AIM single board computer. My Avatar/logo on this forum is of the great predecessor company, North American Aviation which built the P-51 Mustang of WWII.