if you are sure about the 0 deck height then .027 is probably OK but you would normally want .030. Did you check to make sure to rock the piston and check the high side to make sure there is no popout? Your pushrods should be fine if running the stock cam but if you are changing cams you should check the geometry, also you can measure the base circle with a caliper to see if it is close to the stock cam that also affects geometry. Piston to valve clearance you need to measure if changing cams to one with more duration or tighter LSA. You want .080 min on exhaust and .060 min on intake. You can use clay