A good chance he might not have scoped too deep into SD / Manual / No AC particulars when he was ordering .
That was in place all through SD productions 73 and 74
Probably why no one in the world has an original production 4spd AC SD
(barring any special brass car we don't know about yet)
I could understand someone removing and preserving the oil filter .
But hard to understand why the last 2 guys left it in place - if they ever did an oil change
weird