Advise on M4 total overhaul

I have a G&P m4 crane stock with 11.5" barrel. I have had the gun for about 5 years and only put about 10,000 bb's through it. Today I stripped the gears when I pluged in a new 11 volt lipo.
I want to overhaul it with the best of the best parts .Barrel, gears, piston and head, bucking and nub, bushings and shims, air nozel, high torque motor, cylinder and head, spring guide, reinforced 8mm gear box and spring for 400fps. If you can think of anything else let me know.

I just did the same on my son's gun. I purchased a G&P 8mm rear wired complete gearbox for $110. G&P setups are great out of the box and you will spend way more than that to build one. I broke down the cost of the individual parts price below that does not count anti reversal latch and some smaller springs that you should be able to save fro the old gearbox. That was pricing with the fair value parts that I would trust. If you went Best of Best parts, you could add another $50 to the over all cost. If you want the best, System sell a complete gearbox for around $250. The inner barrel on your gun is 300mm. I have two G&P commando length guns. One has a Prometheus barrel and the other is a KM barrel. Both have done really well. I use a Prometheus soft (Purple) bucking. You really do not want a high torque motor if you do not need to. It will reduce you ROF. Some motors that I would suggest would be a G&P M120 or Tokyo Marui EG1000. They will easily pull up to a 120 spring.

8mm Gearbox $60
Wire Harness $25
Gear Set $45
Piston kit $40
Cylinder kit $40
Air Nozzle $10
Main Spring $15
Spring Guide $10
Total: $245

Or....

You can do something like THIS, b/c evike has already done it for you. (I don't wanna hear anything bout Evike sucking Joe!!!)

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back wiring, yes?

If not then here's the front wiring

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Everything you need, and won't die when you connect a Lipo to it... and for you neigh-sayers out there, I've seen 3 of these come out of the box and work incredibly, so hush it!

and for the motor, you can go with [You must be registered and logged in to see this link.]

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so I agree with the GB. I'd say Systema hop-up unit if it's the correct one or two piece unit. Madbull or prometheus 6.03 barrel. thats my .02