Anybody know why speedpro states their pistons shouldnt be used in gen 5/6 applications?

I think GM went to metric sized rings on Gen 6, maybe someone could verify?
I guess replacing a complete set would not cause any problems since they seem to be the same elsewise.

We used Speed Pro/TRW pistons in my Gen VI 454 no problem. You just have to make sure to get the correct rings. I think my piston part number was L2465F-030, but don't quote me on that.

Alex is correct. The Gen VI uses metric rings and the GEN IV uses a standard 1/16-1/16-3/16 ring pack. The weights are not the same so if you only use 1 or 2 pistons, the motor will be out of balance. If you use all eight, just make sure to balance it.
Eddie

Get what ever pistons you want .BUT make sure that they don't have metric ring sizes,the metric piston rings will cost you plenty. The standard ring sizes are very affordable. JOHN

The ring thing is all? I do have the "metric" rings right now on my 454HO shortblock, its really the oil ring that is different - its "shallow". You would think that the ring package alone would not make the piston "incompatible" with the Gen5/6 blocks.

I actually was looking at the L2465 pistons for my motor, found a new set for cheap, but I dont think they really have enough valve relief for my cam.