Bill,
Every different VW engine configuration has its own code, i.e. for 1.8L: the JH (as you know) is a solid lifter, big valve, 8.5 comp, CIS engine. The GX is a hydr lifter, small valve, 9.0 comp, CIS/CIS E engine and the RV/PF are hydr lifter, big valve, 10.0 comp, Digifant engines.
The big valve, hydr lifter heads were used on the Golf GTI's and I wasn't thinking in terms of updating/backdating but whether, technically, the cams between the different valve style hydraulic heads were interchangable or were they even the same cam..
I have a spread sheets that details the different engine codes and tranny codes that I would be glad to email to you if you are interested. Just let me know your email.
thanks