Unless you are going with some serious boost, I doubt you want the iron heads. You can get 317s super cheap all day long. The LQ9 has 317s too. I wouldn't use them on a 5.3 though, compression too low. What are your goals with your engine?
Also you should have 799s or 243s if you have a NNBS. Those are hard heads to beat on a 5.3.
1969 Chevy RCLB C10 350/TH400 SOLD
2007 Chevy RCSB 4.8 4x4 LS SOLD
2008 Chevy RCSB 5.3 4x4 LT SOLD
2010 Chevy CCSB 6.2 4x4 LT SOLD
2005 GMC CCLB DRW 6.6 Duramax 4x4 191,000 and counting
2013 FORD CCSB F350 6.7 Powerstroke 4x4