I decided to do it myself because I could be in control of the final result. Also, I have had pars lost by the professional platers in the past. In the case of the 1974 260Z if they loose a part it could be very difficult to replace it.
The Yellow Chromate was as follows:
200 grams Sodium Di-Chromate crystals (purchased on ebay $20.00)
2.6 litres de-ionized water (super cheap auto)
15 mls sulphuric acid.(local battery supplier)
After zinc plating dip the item in the chromate for about 10 seconds then a quick dip in de-ionized water as a rinse.(just a quick dip - don't slosh it around or you will wash off the chromate)
If you want a darker or richer yellow colour give it another quick dip in chromate (5 -10 seconds) then in the rinse again.
Hang it up and let it dry. Don't touch it until it is completely dry. Best to leave it for 24 hours.
I have re-plated parts such as the fuel cap, fuel filler pipe, bonnet catch, door locks, door lock striker plates, most of the specialized bolts, nuts, and washers, hand brake mechanism, under bonnet brake and clutch pipes, and dozens of small brackets and fittings. I also stripped all the metal parts off the internal heater/air con system and re-plated them. Some are yellow chromate and some are silver zinc finish.
I am using a Caswell Zinc plating kit but the Janes is probably just as good and cheaper. I have some of the Janes zinc anodes and they are cheaper than the Caswell anodes.
In my case I am re-plating everything that was originally plated. Some parts are yellow chromate and some (like the door locks) are silver zinc. Janes and Caswell have a blue chromate solution that also works very well and produces an excellent silver finish with a very slight blue colour in it. The Janes is much cheaper and makes a greater quantity.( If I could work out how to attach pics to this thread I would post some.)
You need the chromate dip on the zinc as it is the protective coating for the zinc.