As for condensation in the exhaust system, that is natural, (especially in high humidity areas) if not driven long enough to heat expel it (all short trips - little heat).
Do the service replacement mufflers have weep holes drilled?
Does yours have bumper exhaust outlets?
As for the heat riser valve itself, there would be no difference if mounted on either side (duals).
The way cataloging reads - FYB
1955 FORD - ?
1956 FORD - RS
1955 BIRD - LS
1956/57 BIRD - RS
Everyone run out to the garage and report ...
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