What was the flybar for anyway? The flybar performs three basic functions stabilization, amplificationof cyclic input, and resistance to pitch up in forward flight.

Stabilization: While hovering a wind gust may try and move (tilt) the main rotor. The flybar will be differently (less) affected, and the linkage system will adjust the pitch on the blades to resist the change.
Amplification of cyclic input: When the swashplate tilts and moves the flybar, aerodynamic forcesimposed by the flybar paddles change the spinning plane of the flybar, and again through a series oflinkages this then changes the pitch on the main rotor blades. This means the servos work less hard toachieve a cyclic input.
Resistance to pitch up in forward flight: In fast forward flight the blade advancing into the airflowcreates more lift than the blade retreating in the airflow. This causes a pitch up motion of the helicopter.The flybar again tries keeping in its own plane of rotation, and through the linkage system adjusts thepitch on the main blades to resist this change.

So the electronic components of the system take over these tasks from the flybarSo why ditch the flybar and change to a flybarless head setup?Flybarless helicopters have arguably better all round aerobatic performance. But they are also great forscale models, aerial photography platforms, etc
Advantages include:

Less rotating mass
Lower drag
Combination of longer flight time and better 3D performance
Less mechanical complexity
Infinitely tunable flight characteristics, including improved stability if desired
Looks cool!

What is required:

The Flybarless Head Itself It is ideal to purchase a custom designed flybarless head for your size of helicopter rather than try and modify an existing setup. There are several reasons for this:

The geometry of the head is important
You are purchasing a product that is known to work

Flybarless Electronics You require a system to take over the role of the flybar. There are two and three axis units on the market. For general flying a two axis unit (meaning you still require your own tail gyro) works very well. For 3D flying there are advantages of three axis units, however the two axis ones still hold their own.A two axis unit essentially contains two heading hold gyros (left/right and fore/aft cyclic). A three axis unit adds a tail rotor gyro also. Much like the way a traditional tail rotor heading hold gyro works, the cyclic gyros have the ability to stabilize the rotor head from wind gusts, etc.It is possible to fly a flybarless helicopter without electronic stabilization. However, the task is much easier with the help of an electronics package. You would not fly your helicopter without a tail gyro, would you?
Servo Selection Fast digital servos are preferable. But again, depending on your flying style,any reasonable servo will allow you to experience the flybarless feel.

In Flight: Flybarless helis can be set up to behave in an almost unlimited number of ways. With a flybar,it was time consuming (and expensive) to try a variety of flybar lengths, different paddles, and flybarweights. With the electronic flybar it is simply a matter of changing some of the programmableparameters in the unit itself and you have a whole new feel to the helicopter.There are some further flight differences with a flybarless heli. The cyclic controls now command acyclic rate from the rotor head. So if the helicopter is on the ground and even a small cyclic command isheld, the cyclic servos may move hard over to try and achieve the commanded cyclic rate. So it isimportant not to add cyclic control until the helicopter has lifted off.Autorotation performance is overall improved, but somewhat of a different technique is required torealize this increase in performance.