Here is a pretty good article from the VW camp on rebuilding the Weber 48 IDAs. The same procedure would work with the DCOE side-draft carbs, too, since they are pretty much the same.
If you prefer to have someone else do them, Jeff Palya of Paltech carb rebuilding would be a good person to use. He does a lot of British Carbs (SU Type) and he is THE expert on the Hitachi SU for Datsun 240Zs. He has done the Datsun work for me in the past on my '72 Z. A real good guy. Visit his site. He has a unique plating process that make these carbs look great.
Anywhoooo..........here is the link. Enjoy.
How to Rebuild Weber 48 IDA Carburetors - by Aircooled.Net VW Parts