Headlamp internals

Yes  3 grommets , 1 each for the loom, speedo cable and trip winder.  Looks like a shell for a coil ignition   bike with the PSR8  switch.  The tricky things to find are a  reliable and complete switch  with its plastic thread undamaged and correct bezel,  A speedo cable with the  6" long heavilly armoured top outer  and dimensionaly correct inner cable projection, An orriginal ampmeter  with rubber gasket , a 120 mph chrono speedo with screw on bezel and intact trip mechanism,  a Lucas medallion. and a headlamp with pilot and a decent light beam.  All of these items can be bought as  pattern spares but in the main  the quality is well down on the orriginal bits.

Front hole is speedo cable. Next is trip. Rear is wiring. All of course need rubber grommets.

The Lucas medallion is I believe available for the top centre hole. I believe it's supposed to be retained by a bezel.

Those lamp shells are almost irreplaceable. Don't lose it!

Seems to me a bit unlikely that you will be able to find the correct grommets  from old  stock? , even if they exist they will be well perished ,I was able to look at a NOS  boxed complete headlamp and they were on their way out. I expect you will be able to buy a box of assorted grommets and if one size is completely unavailiable cut 3 discs from an innertube and superglue them together  to make your own !!

need to get a new ammeter for 12V. Ammeters measure amps, they don't care about the volts. Also if the amps are reduced as the voltage is increased then the Ammeter will read a bit lower. On the other hand Ammeters are notoriously poor items so probably you need a new one anyway.