408 windage tray

There should never be any washers under the factory bolt heads. They should be used between the tray and the bolt head if needed. For a 318 you should not need any washers. I've just swapped bolts and installed the trays on them before...

As far as telling the stroke. If it's together... Take a ruler and stick one end on the piston when it's all the way down in the hole. Note the distance to the deck. Then bring it up to the top and note the distance. The difference is the stroke.