It's been a LONG time, but I had a Rev 6A 500 that I installed an 8372B 2Meg agnus in. As I recall it involved populating the motherboard with 4 more (256x4) memory chips, changing some soldered jumpers, and possibly a change to the A501. Then you had an A500 with 2 Meg Chip!
Sorry if this was OT. The hack came from Amazing Computing in the early 90's I think. They also had a version for the A2000. I would like to see that, BTW if anyone still has it.
Jeff