Why talk about it at all if it's fine and dandy..?
Can you let us know where it stops advancing? I've never seen one advancing past 3700, just curious. If it stopped there, then I'd say you're in a good position, no more changes needed other than turning the dist. for more peak timing. A 12 degree advnce sounds good and I'd try it(aiming for 35 total of course.)
The guy above said you need more timing plain and simple. Mainly because 24 total is lame. You might as well just pull some plug wires off on top of it.
Vortec headed combos make peak power between 32-26 degrees. It's not new ground we're walking on.
Also.. I don't like the 10-12 base number just because mine runs clean locked out.