Hi Paul, Welcome to EAB.
I have upgraded my A600 with an A604. It's a 1mb chip ram upgrade that also allows you to add an Indivision ECS and USB module at a later date. I bought mine from
http://www.amigakit.com/
I also use a CF adapter and a 2gb Cf card for a HardDrive. I have cut the case and mounted the adapter over the PCMCIA port allowing me to change cards without opening the case (again).