click here if you have adobe acrobat and turn to page 3 and you will see all the spring bushing combos for your mechanical advance. MSD tech generally says you want the fastest acceleration ramp possible without detonation for maximum power.
Your current settings might be just fine, but you may just be too advanced. You might buy a timing gun and learn where to mount a new timing pointer. This is probably the best first step since that info is necessary before mucking about with springs and bushings. Once you find TDC and mount a pointer, you can then run the engine and use the timing gun to see where you are at. One starting point might be 10-12 degrees initial advance and 34-36 total advance. On a perfomance engine, it is usually better to set total advance. This means you would rev the engine to approximately 3500 rpm and then set the timing. You can then work backwards to set initial by picking the correct bushing. If you chose 36 as total, then you can get initial from this chart I believe. Silver is probably a good starting point and I think that is the one installed as default.
red.....36 - 18 = 18 initial
blue....36 - 21 = 15 initial
silver..36 - 25 = 11 initial
black...36 - 28 = 8 initial
I wrote a little more about this if it interests you here
http://www.cobralads.com/butcher50.html
hope this info is useful
Andy