Here is a cross reference for different fuel pumps:
http://www.fuelpumps.com/page.html?id=2
Searching through I get the following matches:
AC/Delco EP274
Delphi 25337782
Delphi FE0052
Ford E5ZZ-9A407-A
GM 25116975
Hella H75010041
Punching in their search engine the Walbro 521 is used in 1985-1986 Mustang 6 cylinder 3.8Liter... This crosses to
Airtex E2061 which you can get at many auto parts stores. The strainer looks like it might be an Autozone FS220 and the filter is either an FF3419DL or FF3330DL. Total will be around $125 plus tax.