WHY? This is a DOS based machine. Cannot replace BMDC unless you decide on a new control. It runs at a fixed bus speed. Thus mother board has to run slow like a original baby pentium or later 486DX. The BIOS on these older mother boards will not like anything over 504MB. typical source is dumpster diving. Programs on these machines are tiny.
EMI-inc.net can sell you a all in one half size mother board what plugs into a back plane that also accepts the BMDC. Cost is your left leg (high).
George