I have not tried this myself, but from what I read the opening and closing of bridges does not seem to be difficult.
To open a bridge you just need a sharp knife and light force.
To close a bridge you should use silver paint (the kind that you buy in a pen shape). If you happen to put paint where it should not be you can clean or scrape it off carefully.

Now to your problem. I do not think your Duron will run fine at 1.1V at stock speed. However you should probably run fain at 1.3V at stock speed. That is ~66% the heat that you do with stock voltage.
Your duron runs at ~30-35W now (depending on speed etc), and going to 66% of that you might be able to go passive.

Nice to read that some things are working.

Exactly what CPU are you using? (Preferably with production data etc).

I though that most Durons did have 128k L1 and 64k L2 stock.
Is there really any Durons made with part of the cache disabled?

I don't think any CPU is locked to a specific MHz number. However mony CPU's have locked multiplier (some can be unlocked through hardware mod). It is likely that your CPU can not handle that high speed or your motherboard can not handle that high FSB or that high CPU speed.

I hope to hear more about your progress.