I wouldn't pull more timing out thoughout the entire rpm range. You can run more timing in the lower range where you're not making as much boost. I'm not sure how much boost you have at 3000 but the Cobra only has about 3psi. With that boost retard that I link you could set it up to pull 1-3 degrees of timing per psi of boost. If you are making 13 psi and set it to 1 degree it would pull a total of 13 degrees.
So say you have the initial timing set to 14 degrees and you have another 20 in mechanical advance set to be in by 3000 rpms. If you are cruising at 3000 rpms with vacuum you'll have 34 degrees of timing. If you jump on the throttle and have say 3psi timing will be pulled back to 31 and so on. Once you are at 13psi you will have 21 degrees. This will help in both the lower and mid range power as well as help keep it from detonating.
Now this is in no way a replacement for an intercooler, I'd suggest getting one when you can afford it but it will help you run pump gas without one and is a lot cheaper.
On a side note what's with the dome piston? How much static compression do you plan to run? With your static compression of 9:1 and 13psi of boost your dynamic compression is around 16:1.
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