Difficult to install....no, with the proper kit. Difficult to tune....yes. Follow the directions and whatever info found on line. You may even have to replace the jets. Get a vacuum gauge, it is indispensable for tuning carbs and diagnosing all sorts of engine issues.
A properly tuned Weber is a great upgrade but one that isnt can be a pain. When you do replace the Carter, you need to do the Nutter bypass and eliminate all the now useless crap. All the stupid solenoids, half the sensors, the ECU and a grocery bag full of wiring can be removed. All of it is there to run the Carter. There are separate sensors for the gauges. Get a FSM and you can see what all can be removed.