I have run into this problem up here in Maine every so often when we have to change out oil pans due to all the f'n salt they use in the winter on the roads up here. To the best of my research , there are 3 series of oil dipstick tubes for the 7.5 in these F350 trucks(1987-1997 F350 7.5).
the first was:
1. E7TZ-6750-A
2 F1TZ-6750-A (what these trucks took stock) 91-95
3. F7TZ-6750-A 1996 and 1997.
The problem that I have run into countless times is that none of these oem oil dipstick tubes are interchangeable and, while there were several aftermarket oil pan sources (the pan for the 1991 series is designated FP18B) I can seem to find any aftermarket choices for the F1TZ-6750-A tube. All of our existing pre swap tubes come out as rotten as the pans are. The F7TZ-6750-A series is still available from Ford but aren't even close both on tube diameter and exhaust manifold mounting and will not work with the 1991 series oil pans.. Does anyone have any hidden gems of knowledge of where I could get a few of these either oem or aftermarket that will work with the aftermarket FP18B oil pan?

 

Lisa,
on my 89 I ended up ordering a tube from bronco graveyard I believe. The diameter was right, but the length was not. I cut it down to the right length and had to re-bend it some.
Its not an ideal solution, but it does work.