parts needed to go from 3 to 4 speed

All you will need is a 4-speed transmission and a shifter this might be a good time to replace the clutch and throw out bearing.
Check out the parts for sale section.

If you are going to do that, and if original does not matter, you'll gain more by going with a 5 speed. You'll need some more parts , but you'll get OD . The 3spd and the 4spd have the same 1:1 final ratio. JMO

A SB Top loader, 4 speed shifter, and speedo cable. As others have mentioned, replace all the good stuff while your there.

Jeff

If you get a 4 speed for a good price and trust the seller, it can be a good upgrade.....any 60's/early 70's 4 speed will keep your motor in a narrower rpm range (easier to keep up power!!)

Beware of 80's 4 speed tranny's as many were just 3 speeds with an overdrive, and are weak!!

As posted if you are going to pay for the 4 speed. You might want to consider the T-5. Depending on the money. If you do go to a T-5 your rear end will be a little low. You'll have to be doing 70 before you can really use 5th gear. The 3 speed cars had 2.80 rear gears. A 3.00 of 3.25 would be better. Going to 3.5 or 3.55 rears make 5th very usable but you really loose 1st gear. You'll role about 5 ft and have to shift to 2nd. Alot of 2.8 setups just don't use 1st gear.

4spds of the period also use a different and now expensive reverse light switch.