The two are completely interchangeable - given the port on the rear carb,
and any distributor can use either carb or manifold vacuum. UK spec cars
used the same 45D distributor from 1974 onwards even though the vacuum
take-off changed from the carb to the inlet manifold in about 1977. The
change was purely for emissions reasons, manifold vacuum gives lower
emissions (and fuel consumption) at idle. Off-idle the two are virtually
identical in the way they affect timing.
To use carb vacuum you will need a carb with a port of course, and plug any
unused ports on the inlet manifold. To use manifold vacuum then you would
need to plug the port on the carb, if one exists.
PaulH.
----- Original Message -----
> Another thought. What kind of distributor is Keith going to use? Does he
need
> manifold or ported vacuum? The original US 1979 used manifold but the
common
> replacement Lucas 41427 uses ported.
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