The chassis man. looks like its about 12" long with spade round rubber on trany end and same as th 350 trany on other.
I found this on http://www.lectriclimited.com/mainpage.htm Search for Buick and your year. I found it as part number 90320 TRANSMISSION CONTROLLED SPARK SWITCH HARNESS, engine harness to T.C.S. switch located in transmission, manual trans.
No vacuum advance until high gear is for emissions, not fuel mileage. The first thing I did when I owned a 72 was disable the TCS. The engine ran much better.