The results of advancing or retarding the cam installation from straight up can really only be determined by trying it and then comparing to the dot to dot installation. There are some general rules of thumb around advance helping the bottom and retarding helping the top, but that's simply not always the case. For a cam that's a really good match to the rest of the set up, hp/torque can be lost throught the rev range when advancing or retarding. So I wouldn't run too far with the 'advance to help bottom' theory.
If you read further up the thread there's an explanation (by moi) of what happens to clearance when you advance or retard the cam. You don't want to use a thicker head gasket to get more clearance - it ruins the quench and can lead to severe detonation. If you don't have the clearance you need (.080" intake/.100" exhaust minimums for engines like ours seeing less than 6500 rpm) you can either change the cam (later opening intake, earlier closing exhaust timing), cut (deeper) reliefs in the pistons, or put new pistons in. If you're really close (within .005" - .010"), you might get by with shifting the cam timing the appropriate way, or a change in rocker ratio. But those will only provide you a very small amount of relief. Notching or replacing pistons is probably the correct solution if you want to keep the cam.
