All "small engine" water pumps will fit on your engine, the differences are on the drive pulley. Earlier ones had a removable pulley held with a nut, later ones had that pulley pressed on. Early pumps are sold without that pulley. So if you have a "late" car and you order an "early" pump you end up with no pulley... But since your R4 is early, there is no real problem, you simply don't use your old pulley.