G60 Conversion - Wiring help

I am in the middle of a doing a g60 conversion on my mk1 and I have come to the dreaded wiring! 

According to the diagram I found online the ECU has two earths. One which connects to "battery earth" and one which should be connected to the side of the cylinder head.
My question is, would it cause problems if I just connected to two earth wires together and connected them to the same earth point behind the dash??
I am trying to hide as much of the wiring as possible and I have the engine loom pulled into the cockpit and so it would be a lot easier to connect both wires in behind the fuse box rather than running the wire back out into the bay. 

Does the "cylinder head earth" definitely need to be connected to the back of the head??
And if so why??

Thanks.