Norton 16H wheel rims/spokes

19" tyres.  40 spoke holes, but cross check by counting the numbers of holes in your hubs! Chromed rims, black painted centres with red coachlines.  Sounds like you need a manual - the WD 16H manual is on the wdnorton web site.

.. they're all 40 hole rims on Nortons - "proper" ones anyway! The rim should also be pierced correctly for the hub layout.

Talk to Central Wheel who can supply everything you need including painting the rim centres although that isn't cheap. I've gone for the cheap & cheerful option from them for my ES2.

http://www.central-wheel.co.uk/

The spoke specifications are:

Drive side: 8/10 i.w.g. butted spokes, 8 1/32" long with head angle of 90 degrees. 

Timing side: 8/10 i.w.g. butted spokes,  8 5/32" long with head angle of 90degrees.

Spoke pattern is 1 over 3.

Rims were WM 2 x 19 and 40 hole

My experience of Central Wheel is that they do shortcuts that suit them and not the customer. So for the late rear disc T140 they use 2 lots of 20 spokes instead of the factory 4 lots of 10 spokes. The difference is the head angle, by standardising on 2 instead of 4 angles the spokes are easier to make but then do not sit right on the hub for 1/2 of the spokes. There are better wheel builders around, look for ones that do their own spoke hole piercing.