So you have a revision 8 board which is a 500+, which will give you 2MB chip just by purchasing a 1MB expansion for the trapdoor.
Never had any success using a gary adapter RAM expansion with the 500+, better off purchasing Toms or kippers 8MB addon.
New and cheaper than what you are looking at.
http://www.kipper2k.com/amigaforsale/index.html <--- go hear :-)
