I do not know if you can get the grey tube but maybe use black if needed.
Simply cut the old one off carefully, so you don't nip any wires.
If you use a very small jewellers flat screwdriver - you can release each wire as it enters a connection block.
Best to do a drawing of what goes where first.
Then slide the new cover on the group of wires. Put wires back into connector and make sure it is correct way up and the little tab on the wire end is up so it can engage the connector.
Pull each wire to make sure it has been secured into the connector block.
Connect to the loom and you check operation to endure its all good. This can be done with a voltmeter or even just a wire and bulb.
I don't remember the loom on a 70 model but the basics are all the same.
Some looms will actually require you to split the loom where it branches out and often includes wires that are soldered together. That is a pain but just takes time to resolder.
Just make sure any soldering efforts do not shorten any wires too much, as that can cause problems if the loom becomes too taut when installed. Esp around the headstem ends.
Don't forget to inspect each wire for faults, burn marks, corrosion or brittleness. Also clean them and the ends well.
Any areas that are not covered in tube, use a self amalgamated tape on. It self seals and provides a water tight closure.
Hope this helps.
Feel free to ask anything else.
What model is it?
Tx 500?
Cheers Phil