Classic army SD6

Well, I mentioned earlier that I had been scrimming with my brothers mp5..Its an B@T classic army mp5 sd6,at least thats what it says all over it.Now first off Im not sure who manufactures this,B@T or classic army or both?Is it a clone?When we looked for upgrades,B@T and CA have different part #'s for everything,yet B@T doesnt seem to have a site.The best I can tell,this has a hardened gearbox and can accept upto an M130 in stock form with a spring ,piston head and cylinder upgrade.

What we found(still new to airsoft),Was a complete gearbox from systema that can accept upto M150.
http://www.airsplat.com/Items/AC-UPI-SMP-150.htm
This is an 260$ option.I did a little more research and found that to do it ourselves,it costs nearly the same thing.
So,Is this worth it or should we buy everything seperate and do it ourselves?Were both mechanically inclined and need to learn it eventually.But how good is this price to you,and is it a product we can trust?

Also,the next upgrade will be a tightbore barrel..All we can find is a 6.04 but would like to go down to a 6.02..Is this a feasible option and could someone please point us in right direction if so.

We use .2 -.25g for this and its not to bad .But realistically were getting around 65 feet of accuracy out of it in stock form.This is consistent but subpar IMO.It shoots alot farther,but we can't expect it to hit with even 80% accuracy so,65 is a good #..

What we are hoping to achieve is around 450+ fps with a tight grouping around 130-150 feet.This would be perfect.Any help on this is appreciated.Money is an issue.saving up isn't so bad but the cheapest most reliable setup is ideal.Ty in advance!

EDIT:Forgot to add..It comes with an eg1000 motor or an = to it..Will we need to upgrade the motor with a m150 upgrade?ROF isn't an issue for us as neither is trigger happy anyways.But,consistency,distance and accuracy are important and would like to concentrate on these 3.I notice now to get consistent shots you have to be in full auto.Is it possible to get the same consistency in semi,or even burst as the 3 shot trigger mat be considered in the future.

So,I found the 157 page mod guide here somewhere and took a quick look at it.I think according to that a M130 would be the way to go.I scratched the full gearbox as I now know I don't need it.I think changing the cylinder head,spring guide, piston and piston head will be enough because he already has high torque gear setup,metal bushings a nice airnozzle comporable to most aftermarket ones,a reinforced gearbox.eg1ooo and a 8.4v 2000mah battery.

Still haven't found any info on who actually makes this and can't find a tighter bore barrel other than 6.04.I have found several barrels listed with just the length,but im not sure yet how long this one is.It did come with the suppresor and the barrel extends into that but,I may just end up measuring I suppose.Still concerned if these are all threaded the same or atttach the same,Is the length the only thing I need to worry about?

Avoid the Systema GB´s like the Plague !!!!
Nobody, and I mean Nobody will ever convince me otherwise, these boxes are the biggest money making marketing gimmick that Systema ever came up, Overpriced, substandard internals, and almost guaranteed to dis-appoint.

At the M150 Level, I would recommend that you invest in the Systema Magnum motor, with hardened Pinion gear.

Check the Recommended performance level tolerances for the Torque Up Gears that are already in the Gearbox.

Barrel length is not a Problem, if you insist on a 6.01, buy one that is longer and just cut it back.

Piston, Piston Head, Cylinder, Cylinder Head, Nozzle, Tappet Plate will all most likely have to be replaced.

Hop-Up buckling, Nubbing, new cabels, and installation of a Mosfet are also things to keep in mind.

If you have a link to this gun, I would be more than happy to try and track down the Specifics on it.