Those spiral locks!! Oh man, those kicked my butt taking the old ones off to fit new pistons to my rods. I swear next time I'm buying some kind of "special tool" if there is such a thing to deal with them.
I did a "trial assembly" with my engine and then tore it back down for final assembly. Heads, cam, rockers the whole ball of wax. I checked valve to piston clearance at max lift by using modeling clay on the top of the piston. My new pistons are not marked "front" or have an arrow or mark. I had to "think it through" to figure out which way they went.
My engine build thread:
http://www.clubcobra.com/forums/t62454-30&pagenumber=1