According to my manual the part # for a fuel sender unit for a 1975-76 Mark IV is D4LY-9275-B.This is the same number as a 1974 Lincoln Mark IV with vapor tubes.This same number is also for 1974-76 Thunderbird and Cougar with vapor tubes and possibly later years.It also shows up for 1974 Torinos with a 460 and 75-76 Torino hardtop and Ranchero with vapor tubes.Just checking on Car-part.com there is a wrecker in your area parting out a 1974 Mark IV so it might be worth a call or maybe it is still available from Ford as it seems fairly common. http://www.allamericanclassics.com/
Tubais, my Mark Vs have always had bad sending units and they were always the brass ones except for one which was a black foam type which came from a 78 with the miles to empty computer. I carry this unit from car to car because it has never failed me and I also bent the metal rod to give me a little extra gas below the empty mark on the gauge. Charlie.