Stewart - your rebuilder didn't tell you the whole story.
Once the carburetor has been disassembled, it is very easy to glass bead the cast iron throttle body. Carter parkerized the cast iron new. You can get a similiar result by taking the casting to a gunsmith and having it 'blued'. Once the castings were parkerized, Carter painted the castings inside and out with a semi-gloss paint (generally black, however there are a few browns, and grays).
The Rochester throttle bodies have the same problem, but they were not painted.
Baldbaron - if your kit does not contain instructions, look in your factory shop manual. If you do not have a factory shop manual, I would suggest this is an absolute necessity, but in the meantime; go to the local library, and inquire for the 'reference' section. Ask for a 'Motors' truck manual printed about 1950 (a car manual will do if they do not have the truck manual). There is an excellent section in the Motors manuals on the W-1 carb.
One 'trick of the trade'. We do NOT use the thin copper washers under the plugs (learned this trick from the Carter carburetor school instructor!). Instead we apply a drop of blue loctite to the thread of the plug.
If you have questions, call me during normal telephone hours (see bio).
Jon.
