i always do clearances without headgasket. i suggest 60thou clearance, but also check your valve timing as this has a major part.
now measure the headgasket and use 50% crush as your spec. now with some basic math you can work out your clearance..
i normally dont see any issues when building 4g93 engines as the valve pockets are ratherly deep... it only at 305 deg cams and hi comp pisons you have issues
