If it were me I would be tempted to get an old genuine Ford alternator.

Whilst the pattern ones do not last long, alot of the aftermarket alternators seem to be short lived. On both of our XR3is years ago they kept on eating up alternators (Halfords, Valeo, you name it). Bosch may have been OK, but only genuine Ford ones (from the scrappy of all places!) actually lasted more than a year on the pair of the cars which were daily drivers.