The best set-up I've seen is a "piggy-back" of a parallel flow condenser with the original. Do a search for "parallel flow" and "Whiskey Dan". With this configuration, you don't have to deal with fitment problems and is a fairly inexpensive resolution to weakness of the original condenser when using R134 refrigerant. Since you are keeping the system R12, you could end up with a system that operates even more efficiently.

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Sam

84 300SD 350K+ miles ( Blue Belle )