No. To increase cruising speed you have to change the rear axle ratio. The lower the number the faster the the car will go for a given engine speed. Most Tbirds have 2.91 to 1 ratio but some Lincolns around the same year had 2.72 to 1 ratio. You can also change the tranny that has a lower final ratio but I am not sure if there is one lower than what you have already. You can also go with a taller rear tire.

Good points for lower ratio...
increased hiway speed/reduced engine speed
increase fuel mileage at hiway speed

Bad points for lower ratio...
Less torque to get the car moving, longer 0 to 60 times

Why did Ford put lower ratio in the Lincolns?

Can I switch the axle gears in the t-bird for ones from a Lincoln? What models would work?

Lincolns of the early to mid 60's have 430 CID and 462 CID engines of Ford's MEL engine family. These engines had tons of torque so they can handle the lower gear ratio to get the most fuel economy from them at hiway speed. Lincolns got around 10 mpg! Your Tbird should have a 9 3/8 differential as well as most full sized cars of the 60's. I don't know exactly what models you need to look for but any Lincoln from 65 thru 67 should be a good candidate. The differential will have a tag on the front of the differential that will have the ratio stamped on it. It will have several codes but the one you need to look for is "2.72" or "2L72". The "L" stands for a limited slip differential.