GM Approved licensed CD version of the factory workshop/Service Manual and the Fisher Body manual for the 1981 GM Series.
The 81 is unique in its the first year of ECM's.. early car computers.. wiring is different as are alot of the Turbo TA sensors.
Not Expensive .. not a good as a paper manual in the workplace perhaps but price is right and its often easier to study and transport.. or copy a note from etc.