Could probably take a ballpark guess, but I won't. A 4" lift on a CJ7 is probably going to require a T-case drop and CV driveshaft as well as some degree shims (unless you rotate the perch mounts). It's probably best to get the suspension in and the drive line angles set where they should be and then measure for the driveshaft(s) before having them made. Measure yoke center to yoke center with the suspension at a static level position, at full extension (jack up the frame so wheels are off the ground and axles are hanging only by the springs), and compressed if you can (ask a dozen friends to climb on, or I can give you contact info for my ex-wife LOL). Give the measurements to the drive shaft shop in order to get the proper length. Depending on your setup you may need long travel slip yokes (are you planning to use shackle reverse kit?). Another thing you want to decide is the diameter and thickness of the tube you need...
I agree with Spieg8. You need to measure... your distance and your angles. While I don't cover the length measurement, you can read about all the other aspects of a lift in the article linked in my signature block.
Vibration? Bump steer? Wandering? Read the article (sticky) on Steering, suspension, and driveline.
I disagree with the bit about a transfer case drop. That's a band-aid for keeping the stock driveshafts. If you're getting new shafts leave the transfer case alone and get a CV type rear driveshaft, which will handle the steeper angle in the rear.
Not much if any that I found. I just swapped from the 20 to the 44 and using the same driveshaft, although I didn't set the angles right (yet) so I don't know for definite if the shaft length is different. It works, but vibrates from the angle issues.
Don't guess. His measurement will be a good starting point, but don't have yours made until the lift is on and the angles are set. You only want to spend that money once, and shortening is a lot cheaper than lengthening if you got it wrong.
1978 CJ5 5.0HO/T177/D300, '86 D30/D44 WT axles, 'glass body, 31x10.5 BFG A/T, TDK galv'd frame - DD and weekend toy
If I remember correctly (it's been quite a while), the yoke on the Dana 44 sits about an inch or so more forward than a Model 20 (slightly shorter driveshaft). They can use the same Spicer 1310 U-joint (some people like to upgrade to a beefier model).