They might be for 6 inch rods, now that I think about it. I cant find the ones for the 5.7's. But the rest of the piston is the same haha. Coming in at 9.5 or maybe even 9.75:1 should be real good for 92 octane.
These kinds of threads are great when you are trying to put an engine together, and picking parts. A lot of ideas and info in one spot. Here is a really good website for engine combos, although I think some of the HP numbers are a little exaggerated.
http://www.ryanscarpage.50megs.com/combos1.html
Another edit
. I found the pistons I am using with the 72cc heads.
http://www.summitracing.com/parts/STL-H631CP/
These have the correct compression height.