When I bought mine the pins were the correct size but the rings had way too much end gap, I cant remember exactly what the end gap was but it was at least .020" or more, I didnt use the rings but fitted a Hepolite set I had.
If your pins are loose in the rods dont use them. When you say billet rods I take it they have no gudgeon bush, the pins run directly in the rod. Do you have a set of original pins that fit the rod correctly, if you do heat a piston and see if the pin will push in. If it does you could use the pistons with different rings and pins. This of course means you would have to buy new pins and rings which probably makes the whole thing more expensive, alternatively you could send them back.
The ones I put in my engine have done just on 1,000 miles now and so far so good. It seems like they will run ok but time will tell what the wear will be like. I have a set of Hepolites ready to put in if these ones cause any trouble.