Using standard components, yes, 2.5gm is the max. You could stretch it to 3gm, maybe more, with a custom plunger and sleeve. I think 6-8 might be expecting too much. The real limit will be the clamping pressure vs your part surface area. If you install a custom PLC (heck, a raspberry pi would do nicely), you can "double-shot" your parts to increase your volume, but again, the limit will be the surface area.

So, what is the surface area of your part? The rule of thumb is around 3 tons per square inch, depending on the resin you may require more (up to 5) or less (2-2.5 tons). Since a new machine is limited to 5 tons, you can't really make a part much larger than around 1sq". I have made a 1" square with 1/8" radii in the corners successfully, and I have also managed to get it to blow the mold apart slightly. Maybe I did not have enough preload on my mold (see below), but that gives you an idea of max size.

The clamp already has a toggle action, with leverage, etc. It's a pretty complicated system, with quite a few parts considering the size of the machine. It's because the one air cylinder both closes the mold and also injects the plastic, and it does it in a mechanical sequence. There is no physical way to push material without closing the mold. As far as increasing the clamping tonnage, the levers in the linkage will be one limiting factor (like a fuse), and the tie rods will be another limit. The way it's designed, with full clamp force, the tie rods already stretch .018". If you want to double that, you'd be stretching almost a full millimeter, and I doubt it will last long like that.

Moving on, the rod holding in the barrel has a screw in one side; you have to loosen and remove the screw. It's like a pinch bolt, IIRC, so the screw pulls the rod (which has a flat taper on one side of it) into the bottom of the barrel, thereby pushing the barrel up. Once you loosen the screw, you can push on it on the screw side (maybe tap the screw after one turn loose), and the tapered rod will pop out the other side.

I already have a manual, and I also downloaded a PDF from this forum; it had a few bits of information that mine did not. If your version has more information, then I'd appreciate it, otherwise I'm set.

I have a sales brochure, and that lists the specs of the plungers.