I think from memory my old FC wagon used to sit on around 3300 rpm ish @ 60 mph ( standard 3.89 diff with crossply's ) so 3.55 would be about right @ 3000 rpm @ 60 mph.
Depending on your rolling tyre diameter Reddo I'd guess a 3.36 will bring it down to around 2700 rpm ish @ 60 mph.
Sometimes those little 149's can go just as good as a 186 can given the right engine performance enhancing modifications .