The later fuel pumps have a breather hose fitted to the filter to, as I understand, prevent cavitation.

This implies that the early pumps may suffer from cavitation.

So my question is:- Will the later filter fit the early pump and, if so, where does the breather hose go to?  

Paul.

Only the early larger early pumps had that hose.

No, the filter for the later pumps does not fit on the early ones.

To use the newer type of prefilter with breather you must also change the rubber mount, as the newer
prefilter with breather have a smaller dia than the old one.
Others that have done this change have blinded the breather at the prefilter w/o any problems.

For what I've seen, the initial pump installation design has a suction strainer which covers all the pump´s lower side, if the strainer gets clogged the pump will run dry, that not only will shutdown the engine due to fuel starvation bu also will destroy the pump due to lack of lubrication and refrigeration, the small hose is intented to guarantee the minium flow required to avoid a catastrophic pump failure, but the engine will shut down.
In the newer design, the pump is settled more deeper in the tank and the strainer do not covers all the pump´s lower face, letting a small hole uncovered, this small hole is the minimum flow suction port that replaces the hose in the initial arrangement.
That´s my best guess.
Best regards
JAP