The weber carb is very easy to set-up as well, only two adjustment screws!
I've had them on two landrovers.
One thing to watch out if fitting one is to make sure you have full throttle movement, my first one didn't. I think the throttle spindle rotates in the opposite direction on the weber to the original zenith and even though the original link rod will fit may need adjusting in length.
Carb is last on list of things to check on a tune up though.
As HF said start with compression test, then check valve clearances, next is ignition system.
Only when all the above are sorted should you try to adjust carb.