YEAH! All I have are '+'s on the top of my pistons... What luck! It is hard to see, but at full resolution it is apparent. But, what group is that? It is not the weight group as they are all '++' marked on the inside of the piston and I matched that correctly...
(I'm soooo happy I took lots of pictures!)
Just checked the engine... looks like I'm in mismatch. #1 & #2 cyls show a '0' stamped in the same place the height group is stamped (logically the place to put the diameter group stamp). #4-#6 show a '1'. If I were a betting man I would now say I have two in group 0 and four in group 1 with all the pistons being in the same group. I can assume that since I had 5 pistons and 4 cyls from the original engine that '+' means group 1 for the pistons as that would match my group 1 cyls.
Here, it looks like, I have two pistons from group 1 put into 2 cyls of group 0. The specs on pistons do overlap for the two groups while the specs for the cyls do not. Now... what are the consequences of getting mismatched like this? Closer piston to cyl wall than designed means what?
Best regards,
Michael
PS I can't imagine the pain of trying to make a complete matching set from a box of singles...
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Michael 
'82 Euro SC 'Track Rat' 22/29 Hollows, 22/22 Tarrets, Full ERPB F/R, Rennline Tri Brace, Glass bumpers, Pro 2000's, 5 pts, blah blah blah
'13 Cayenne GTS