In the A500, you had the Agnus chip which addressed 512KB of CHIP mem. The late models of this had the Fat Agnus which would address 1MB of CHIP mem. Then finaly you had the A500+ with the Obese Agnus which addressed 2MB CHIP mem. (As long as you had board revision 5a or better upgrading wasn't too hard
Some of the late models of A500 (late 91?) also had ECS instead of OCS, and some had WB2.04 instead of WB1.3 or WB1.2 (mine came with WB1.2 in early 87!)
AND as already said, there was the slow/fast expansion RAM that you may or may not have fitted... so Gary's spot on when he say's it's hard to answer this one!
BUT generaly if you set 7MHz 68000, OCS, 512KB CHIP, 0KB SLOW/FAST, 0KB REAL FAST, no gfx card options, then you should be pretty close to the original...
Next time ask for the meaning of life or some other easy one