Hmm, I'm going really really far back in my memory, but try

100011

100001

100010

Then try with possibly adding the second bit on.... I MIGHT still have a few of the 6 bit adaptors around here. But you aren't going to hurt anything if you get it wrong. You might get crazy sync though...

The important part is to power down and then make the change then power up and see if anything changes.

You'll know you have a good setup when you get a boot image AND in the monitors panel you can select at least 1024x768 in thousands or millions of colors.

Let us know how it turns out.