Have you ever seen an oil pump spring attatched to the oil pan instead of the pump? Seen one today. The spring seemed shorter than the ones I have seen attached to the pump.
It seems that Ford experimented with this too. On mine the spring was sort of "rolled" into the bottom drain plug ring. I pulled it out but as with most of these sort of "one assembly" sort of arrangements, the spring wouldn't go back. So I used the little bar notched for the spring as is found on most of these.
Yep, ran into that on my dad’s car just a couple days ago. It has a ‘28 pan with the pan clean out plate so I figured it was a ‘28 thing. What year is the car you saw it on?
I have that pump spring in my 29 engine, to remove it, it just threads out, to refit thread it back then tap the bottom coil down with a screw driver, makes a click sound when bottomed out.