If I was you, I'll ask for another revision, mate. The revision #3 is plagued with bugs and is not reliable.
Prefer a rev5 if you want to seep using only 512kb chip mem (and 512kb slow/fast ranger mem) and/or ROM 1.2.
If your goal is get the best possible A500 get a revision #6 (up to 1Mb chip RAM without special hardware, just a simple hack), or even a 8.x board (hard to find in USA, specially the NTSC version), which is the 2Mb chip RAM possible board.
Any way, good luck with your search!