799 casting is a preproduction ls6 head, there is 2 casting companies that gm uses, one is in mexico and they are a sand cast version, the other in canada is a premold version. the 853,806, 863, 817 and 799 are from mexico the 241, 243,706,035 are from canada. I have seen the 799 casting and they look identicle but they flowed a little less than an 243 casting, I think if ported you will see the same results as the 243

as stated 241 castings are the best flowing 5.7 heads over the 853's and the 806. 706 5.3 heads have smaller intake vavles 1.89 vs 2.00 on the 5.7 heads. CC on the 5.3's is smaller, if you get some 5.3's you'll want them ported and outfitted with bigger vavles to get the most out of them. due to there smaller CC they yeild a 10.8 CR IIRC.