Alright!!
I've finally installed all the parts and got my Tar back together. It was a hella lot easier than I thought it would be.
SO, here's the reports:
-Prometheus Purple Hop-up rubber (Fits, but kept the stock nub cause it looks to be of good quality)
-Prometheus m16a2 Air Nozzle (Works as I said before. I was a little disjointed with the compression it gives, but still a hell of a lot better than the stock ARES air nozzle. I think I will try a different air nozzle later)
-ARES Cylinder Head for M60 / MK4 (It works, perfect fit!)
-ARES Spring Guide for G36 / M4 / SCAR / L1A1 / M14 / UMP AEG (Holy god, it fits and works 100%! For those who lost/broke your original spring guide, buy this one! It also has ball bearings preinstalled!)
-Guarder Infinite Torque-Up Short Type Motor (Insane trigger response! Increased ROF nicely. No more semi locking issue! I've out 4000 rounds through the tar and no semi-auto locks yet!)
-King Arms M4 Metal Hop-Up (Found it that it installing it would be a hell of a lot more trickier than I though. Not only do you have to cut the bottom part off, but the size is off. Don't bother with a new hopup unit. I'll just dump this into my HK416 when I get a chance

)
-G&P EP Power 11.1V 1200mAh 15C Lithium Battery (Fits very well! lots of clearance left. INSANE ROF!)
-LT War Pro Max Hard Piston (As I thought, I had to file down the first and last tooth on this piston to get it to fit. After about 2 minutes of filing work, it fitted perfectly.)
-Prometheus POM Piston Head w/ Bearing NEO (Fits perfectly, no issues here.)
-Madbull 509mm 6.03 Black Python Tightbore Barrel (Fit in the stock hop up unit, no problem at all. No mods needed.)
-King Arms Normal Torque Flat Gear Set. (I think this solved my double feed issues I was having before. Other than that, no mod needed. The gearset works well. Make sure u shim the sector gear decently high though.)
-Active Braking Mosfet (Works!)
-PDI 170% spring (Fits and works no problems)
So after all the upgrade parts, the gun is shooting at around 390fps and ROF at around 20RPS (Rounds per Second).
Overall, I am VERY satisfied with the upgrade parts! This ended up a LOT easier than I thought it would be. The only thing that really needed modding was the piston. Other than that, everything fit in fine. This thing is a BEAST now. Can't wait to take it out for a skirmish
I still need to do a proper accuracy test, but so far, from 50 feet, the bbs are crazzyyy accurate. I can hit a quarter 100% of the time.
Only complain is that my barrel is slightly exposed now; the silencer I got isn't long enough
I'll post pics if people ask for it, and if I can find my camera :P
Hope this helps anyone who's upgrading this gun in the future
Cheers.