Have you checked with other SIMMs (or just with 1 simm per time) ?
If the board is really dead, i've seen there is still 202688 boards on ebay for a correct price that will just fit in your case. The integrated VGA (Cirrus logic 5426/5428) seem to be wired in VLB.
I've found in my computer an old capture of the AST user manual (only CPU config page). It was included with my system so the config is for the 202560 mobo(AST Bravo LC 4/33). Sorry it is in french, but if it can be useful for someone ...