First: the Fatter Agnus from A500+ is totally incompatible with any A2000 board but the 8.x. If your A2000 have an OCS Agnus, then it cannot take a 8375 Agnus.
For the crashes, most of the time the problem is the old and tired power supply. Replace it with an AT or ATX unit. Remember the ATX units does not have -5V and can cause problems with video and serial cards.
