My 66 was set up the exact same way. Hurt like crazy to drive it on the freeways!
A steady 65 mph made the little 230 sing like a strained mockingbird. Trying to keep up with the "slow" traffic on the interstate at 70 mph was close to engine homicide.
A 292 engine and new process overdrive tranny swap later and now 80 mph is fewer rpms that 60 mph was before overdrive.
Now 70 mph is very comfortable at only 2200 rpms, with at least 10-15 mph of extra cruising speed comfortably available.
Overdrive is WELL worth the effort.
-ftyler
