Guys, I am betting on 170 cc heads myself. They're Eddy PN 6090 Performer heads I bought in 1999. I did have a 3 angle "performance" valve job done on them recently. I currently have them on my 355 with a CC extreme energy 262 cam and they run very well. I will be replacing that 355 with a roller 1 piece RMS 383 short block next year, but I am keeping those heads. Hoping for good results with those small intake runners. My plan is to run a somewhat mild cam - GM PN 1921073. It's the same cam GM put in it's ZZ383. Besides, Grandpa always said: "there's nothing wrong with a little head"