We don't run an idle motor either. The engine idles around 1200-1300rpm when warm, but that's fine for a race car and helps increase camshaft life anyway.
On our headgasket, we normally use the Hylomar gasket dressing to help it seal. So far, it hasn't been a problem on any of the cars we've re-used it(one of them three times, two others, twice). That being said, for peace of mind, you could get a replacement. I just would NOT recommend a stock gasket if your pistons are indeed flush with the block's deck. You ideally will have between .030-.040" clearance there, or slightly less, but not much if revving the engine to 7000 and beyond. Our current engine has around .025" clearance on the tightest cylinder on the piston center line, so excluding piston rock(roughly measured, I'm no machinist).
On our headgasket, we normally use the Hylomar gasket dressing to help it seal. So far, it hasn't been a problem on any of the cars we've re-used it(one of them three times, two others, twice). That being said, for peace of mind, you could get a replacement. I just would NOT recommend a stock gasket if your pistons are indeed flush with the block's deck. You ideally will have between .030-.040" clearance there, or slightly less, but not much if revving the engine to 7000 and beyond. Our current engine has around .025" clearance on the tightest cylinder on the piston center line, so excluding piston rock(roughly measured, I'm no machinist).