The head unit was just a universal unit.
The year I bought it new was,,,can't remember,late 80-early 90's.
The SN89 (Model number)was used on SBC, SBF kits.
I made all the serpintine pulleys,brackets,ect.
The thing about serpintine belts,better make sure they are lined up close to perfect,otherwise they will move.
MBHD
