The original finish is without doubt black anodizing. Attempts to replicate it by re-anodizing here in the UK have not resulted in an acceptable finish. Health and safety issues have also resulted in most jobbing platers closing - the few left are high tech concerns, who will not usually take on auto restoration work.

Personally I have resorted to the use of paint (PJ1 "Satin black case paint") rather than powder coat. If the unit is rubbed down with fine grade emery paper, sprayed with both paint and unit at 70°F or more, allowed to cure for a couple of weeks, and finally lightly polished with a fine grade metal polish, then a very durable and close to original appearance can be achieved. The m/cylinder on 1005298 has travelled over 50,000 miles now in all weather and bug-splatter conditions with no chipping or fading. Just my solution to the issue until a supply of NOS units turns up.