On a 30 pin SIMM pin 1 and pin 30 are 5V DC and that square pin that shorted is pin 1 on the socket. Pin 2 is /CAS.
Burning plastic turns to carbon which is conductive so clean the black goo off with alcohol and see if it is still shorting the 5 volt rail. If all those tantalum capacitors were shorted to ground I expect them to explode so its something else. The power supply should shut down on a direct short.
Well, went and checked - C155 is shorted, along with just about every other capacitor. The +5v rail is shorted to ground somewhere; I'm guessing that probably fried a few things.
Oh well, it will make a nice shelf piece.
Plastic, which is what made the smoke/burning smell; there wasn't any visible metal anywhere nearby, which is what threw me for a loop. I just got back from running errands, so I'm going to eat dinner and have another look in a few.
Basically any Toshiba or Plextor can. XM-5401B, PX-40TSe, etc, etc. I know Sanyo can not for sure (used in some LaCie drives). The CR504/CD600i iirc is jumperable too, using the 2nd from the far right jumper to enable 512 byte sector support. The 300i might also support that, but I don't remember off the top of my head.