Keith Black pistons VS Speed Pro for 318

No need to install pistons to figure deck clearance. Measure how far you current pistons are down in the hole then subtract the difference in piston height between stock pistons and the ones you want to use from the current clearance and you will know where the new pistons wind up.

Plus, the machine shop should tell you what will need to be machined to get to the clearance you want by measuring the block.