Richard,

The current Pro SD Polaroid back will fit. Note that if you buy a secondhand Pro S back you will also need a "P" adapter and these are very rare. A company by the name of NPC also produced backs, but again, these are quite rare.
You will have to make exposure adjustments - some meters (Sekonic)have dual ISO settings which is useful for this purpose.
The Mamiya backs take the 3 1/4 x 4 1/4 inch film packs from Polaroid and Fuji, but for available film stock please see their wesites

By Richard on Thursday, September 30, 2004 - 10:19 am:

I'm contemplating buying a polaroid back fro my RB67 Pro S and would be very grateful for any information on how it should be used.

For instance;

What film should I buy for it seeing as I generally use Velvia 50ASA?

I take it that the polaroid film isn't 50ASA so I would have to compensate with the exposure afterwards?

Are there different polaroid backs available for my camera?

Thank you for your help in advance