I did a 2 meg chip ram hack to my rev 6a 500 years ago. It involved using an 8372B Agnus and replacing all of the 256x4 memory chips on the motherboard with 1Megx4 (including filling the empty slots). Some traces also had to be cut/modified. As I recall it was in Amazing Computing magazine last half of 1993.
It would indeed be much easier to just find a used Megachip:-D
