That is super wrong.
Do NOT buy anything from ESC, quality is abysmal.
Don't bother with the AA chamber, it's a bit hit and miss, in a lot of cases it leaked like crazy, I would rather keep the stock chamber and replace the arm with a GunSmithy one. Masada tensioner is a good option, if not, a standard ML Omega will do.
Maple Leaf rubbers are NOT compatible with bridged barrels, I would suggest an Action Army 6.03 x 300mm inner barrel, DIY spacers made of painter tape or printed and fill the void with foam/scotch brite/damping material. MR-Hop is (imo) the best rubber available right now. Failing that, I think the Modify X-Range series are decent rubbers.
Much than buying some dodgy super expensive, super tight bore barrel that requires cleaning every magazine fired.
The NEMO clone is hit and miss in quality, some are great, in some the guy who put them together forgot to weld the butt plate (yes, it happened more than once). Since you are going to get a shorter barrel, having an enlarged cylinder becomes useless (the NEMO has been designed to work with the long 500+ mm barrel)