[chrismorse]

If the condition of your local roads is “some ok, some terrible”, I would stay with rubber for a driver and not go much stiffer on the bars, springs.
I went with automotion polyeurethane bushings on my old hot rod 914 and they were very rough on the street, primarily due to their inability to relubricate and the subsequent “stiction”.
That said, I rebuilt the suspension on my 308 and used “poly-graphite” bushings and doubled the spring rate. 20 k miles and it rides ~~50% rougher on our humble county roads.
The 74 will only see occasional DE events, so it has Elephant rubber.
Another option is to go with “sport hardness”, or heavy duty rubber. This may give you a bit less compliance, but still offer some road noise reduction.
(Elephant only offered sport hardness for the strut tops and the trailing arms, so, I went with those. The car is not on the road yet).
No experience with monoballs on the street.
chris