Yes, sdram_init=0x0013 should enable 16-bit mode (instead of 32) with 10 columns, those disabling the second chip U4 and detect 64MB. In fact that's what I used to enable 64MB ram on my WL-500gP V2 (I did not touch sdram_config).
If you ever get in trouble by making a typo when entering sdram_init (like I did, silly me :P), you can recover by erasing NVRAM with a JTAG cable.
Here are some pictures and links regarding the issue.
edit: I'm clueless about error you are experiencing though. You said you used Samsung chips, so you shouldn't need any capacitors. In fact I used the exact same type of chip from ebay (K4H511638B-TCB3) on my router and everything is fine.
