The 8372B (2MB Agnus) is pin compatible with the 8372A. I had one in my Rev 6 A500 with 2MB chip ram on board (sold long ago). I didn't do the mod myself, but I remember that it was hard to get the required RAM chips. It is not an easy mod, even if you can get all the parts.
That being said, if I had the parts I would try it on my Rev 6 A500, just to see if I could do it.
