I don't see how the inner diameter of the bore has anything to do with the mechbox...and vice versa. From a technical standpoint that is.
Re. if it's worth trying to turn a pigs ear into a silk purse...well, it's usually not. But it's fun trying sometimes
If it makes you smile, go for it.
Depends on what you want to achieve....if it's great accuracy, the consistency of the mechbox and the FPS out of it is the determining factor. If it's durability, then it's the quality of the components. Sub par mechboxes rarely have either of those two traits.
You'll need a bore up kit for sure...I don't know how long a barrel you can go with one of those (i.e. how much longer than 650mm).
Jugglez (airsoftparts.ca) is just awesome to deal with...ask him, he might know or can message the factory and ask them.