I also did that hack to a rev 6 500. The article was in Amazing Computing Amiga magazine in the end of '93 I think. You have to replace all the motherboard ram locations with 1Megx4 Dram DIP's. You use an 8372B 2Meg Agnus (A3000 Style) and modify some traces on the motherboard.
It works great, but finding a used DKB Megachip on ebay would be a lot easier. The 1Mx4 chips were hard to find back then, and the Megachips go for less than $100.00 usually.
Have Fun,
Jeff
BTW This the above also applies to the rev 6.x 2000's as I recall.
