Power steering pump interchangeability for Audi 5000/100/200

[RJA]

Does anyone know what the difference is between the hydraulic (power
steering) pumps for the '89-91 200's (034 145 155C) and the ones for the
earlier 5000's (134 145 155D)?  I've been told that the only difference is
the pressure relief valve inside, but that they can be used interchangeably.
Can anyone verify that?  I'm looking for a rebuilt pump for my '90 200 and
have found a good source for a rebuilt ZF pump (034 145 155D) but want to
make sure it will work.  Did the '90 200's use Pentosin CHF 7.1 or CHF 11?

-- Rich
   '90 200q
   '83 Coupe GT