As far as K2/K3... very small changes, basically K3's were kinda like K2's less a lot of the bling to save weight.

As far as K3 to 777... There's a whole lot of changes.

- Chassis is different because the engine was moved forward.
- Suspension geometry is very different.
- Rear shocks are longer.
- CG is lower due to the shorter servo tray posts, the servo has less than 1mm clearance before it hits the chassis.
- RX box is smaller.
- 777SP1 adds a stinger protector.
- Servo saver upside down compared to previous versions.
- Ackerman is also different.

Those who have both K3 and 777 say the difference is profoundly noticeable, much so that setup sheets used the K3s will NOT work with the 777. The 777's rear is so finicky in stock setup it's not funny, with sometimes annoying oversteer so you gotta dial it out.

As for the differences between standard 777 and SP1 version, here's a link;

http://www.towerhobbies.com/rcwnews/...-kyoc0564.html

I suggest you get a hex screw conversion kit right away, those Self-tapping screws included in all inferno's have a tendency to back out.