*shudder*

Anyways -- This is the standard upgrade list for Manitoba Ivan:

Prometheus Tightbore
ARS Hop-up rubber
Shredder's Concave Spacer
ARS 3G Piston Head
Sorbothane pad for cylinder head
Trigger Master MK3

Wow - Thanks everyone for your advices!!!!
It is really awesome response!
I was hoping to order everything I need for upgrade in a single company (or max two), presuming it will be eHobby. But it looks like not quite possible... Can I ask just one more thing... please... can you advise me good place where to buy all of that (I think I can base my upgrade on Amos ideas)? Please. don't blame me being lazy - it is not that big problem to check 20 sites looking for AEG, but it is much harder to check 20 sites looking for 6-7 parts...
Thanks for all your help!!!!

I've tried Intellect 7.4v 20C 1200mah Lipo from Airsoft Parts. It fits very tightly but I was able to do it without using gas tube, its too high to fit inside gas tube anyways. I dont think the longer 3 cell Lipo will fit though, so gotta stick with 2 cell.

You're gonna have to shop around.

Ehobby doesn't carry ARS because they're a small niche tuner brand, And the Trigger Masters are a Canadian design/product.

I've got extra rubbers, SCS and piston heads if you're interested.