CCC Energy

I totally agree. I felt like a smithy in the middle ages hammering away on those big cables to make them fit nicely. 🔨
Might also be the reason that plastic DB cases don't work so well... 

This part often causes confusion and people wonder why that fuse is there. Let me see if I can explain.
That neutral wire, which would normally be black in colour, carries only the current required for the electronics of the meter itself. The red wires between terminals 1 and 2, they carry the big stuff. Since that black wire only carries a few milliamps, it does not have to be a very thick wire. It can be as thin as 1.5mm^2. And under normal conditions, that would be all that is ever needed. But you have to cater for what happens under not-normal conditions, aka fault conditions.
Under a fault condition inside the meter, that meter might be dead-shorted from either terminals 1 or 2 to neutral. It is unlikely, but you have to cater for that. In that case, you must have overcurrent protection for that thin black wire, so that the wire itself does not turn into a small heating element that burns down the house. That's what the fuse is for.
The fuse just needs to be sized for (or smaller than) the wire. In this case something like a 5A fuse will be more than sufficient. It is less than the wire can carry, so it protects the wire, but way more than the meter will ever need to operate.
But... you can also just leave the fuse out. But then you must size that black wire for the full current of whatever the upstream breaker is. Since this meter is usually installed right after the big 60A breaker that feeds the house, that black wire must be sized for 60A then, that is to say, it would have to be a 10mm^2. This is what I see most installers do, they just use a thick enough black wire.

I am uncertain how / what I should cut from this expensive battery disconnect to allow 70mm2 cables to be connected.
If someone is willing to post a picture of what they'd done that would be great.

I have never quite understood how you are supposed to get a cable into them. I always cut the plastic to get the cable in. Don't like it, but until someone can tell me how it is supposed to work, that is what I do.

Check SANS requirements, all DC cables must run in steel conduit,not PVC. 
 

I think this latest document from CoCT explains the Inverter size limits much more clearly than previous versions.
SSEG residential generation size limitations (2020-08-14) (003) (4).pdf