Completed the install over the long weekend, thought I would share some learnings...
Photo 1 shows the rear of the fuse box with accessory power terminal circled (fuse 10).
Photo 2 shows the white wire which connects to the negative terminal on the coil.
Alfa/Bosch conveniently supply this with a male connector. Your choice of coil, on my car the factory tacho (brown/white wire) is connected to the coil on the left of the shot.
Photo 3 shows a row of male connectors earthing to the front of the car right behind the headlight, once again Alfa conveniently supplies 2 spares (lower row)
Photo 4 shows the installation of the Speco tacho to the windscreen frame (no holes in dashboard!).
I only needed to drill 1 x 7.5mm hole in firewall right behind the fuse box to pass wires into the engine compartment, this was finished with a rubber grommet.