(LS1 block)Is it 6.200" or 6.125"? I want to use a Mahle Piston set-up, flat-top and whatever other specs to get a 10:7-11:1 comp ratio with 5.3 heads milled .010". Thanks

 

You can use either, but you need to make sure that the piston manufacturer knows how long the rod is so they will know where to place the pin. I would use the 6.125 since they are the most common and have the most brands to choose from.