Can cam support gear change?

3.23 with a 0.8 OD and a 26.5" tire would put you at 2130rpm at 65, 2290rpm at 70.

How's the car handle hills right now at that rev range (1900-2300)? If it can accelerate decently starting from 1700-2000 rpm up a steep hill with mulitple passengers in 4th gear, then dropping to 3.23's might not be so bad.

3.55 would be even less bad, and still get you under 3k at 65 (~2350). 3.91's would be around 2600 @65, and at 3k you'd be at 75mph. Personally I'd pick 3.91's.

If you're at all concerned about how the engine will perform at lower revs, I'd make a smaller change in gear. Even the 3.91's will make a substantial impact to your cruise rpm. I know my car at 2600 is pleasant, but at 3k it's starting to rattle the ears and by 3500 it's annoying for any length of time (I have 25.5" tall tires, 3.91's and no OD, so 70mph is 3600rpm, 65 is 3350). I've got a 408 with a bunch more cam (295 adv) and it will pull from 2k, but it's much happier if I keep it over 2200. The smaller cam I used to run (284 adv) was fine down to about 1800rpm.