You don't need to go to the junkyard to get the fitting for the A/C pressure switch; it is available from several vendors either in aluminum or steel. I don't know if I can post non-sponsor links here but if so, let me know and I'll provide the links. Also, as far as I know, GM A/C pressure sensor used in most LS cars has a fine metric thread. Specifically M10 x 1.25.
The fitting is on the right.
