Hello from Cave Creek AZ

You'd probably have to invest in tooling, fixturing, and/or sub-part manufacturing of the 3/8" to reduce your labor $$ cost. $90 for a good part over a $60 semi-functioning part is palatable. You start going over 3x the lesser fuel senders, customers start looking at other options or just put up with lesser fuel sender.

You pretty much nailed it. Typically when I am performing miracles it is because some one wants the original "built with" part or at least to have an OEM part number that is correct. Building a reproduction sender is actually a lot less expensive than the labor cost to lovingly disassemble and rebuild a 50 year old part. Incredibly I trade reproduction senders for '64 through '66 Mustangs straight across for a rebuildable core. I have dissected the reproductions and they cut a few corners in order to hit the lowest price. For a great many people that is all they need so I have no issue with that. I manufacture reproduction parts too, but only those that can be built to equal or better than original equipment.