Going from a 317 head to a 243 will bump the compression a full point. So it'd be 11;1 or so and that by itself is worth some HP and some associated torque. Since he's already got the 243 heads, that's definitely what I'd run. As mentioned, 243/799 are the same (aside from the exhaust valves being sodium filled on 243s) and 317s are identical as far as port size and flow, they're just a 72cc chamber vs a 64cc chamber.
Once you start getting in to head porting is really when a custom grind cam really shines. Everything in a motor build needs to work together with the cam OR the cam guy needs to know what you've got to make the cam work best with everything else. It all fits together, just depends on if you get the cam first or last. Generally on an NA LS motor that's not hog wild, really all they need is some blending on the short side radius in the intake runners and maybe some porting on the exhaust side. There again, that depends on the needs of the cam and what the intake will do for it. If you start opening up the intake side too much, you'll lose some lower end torque because of a loss of intake air velocity. It goes on and on. Main point being, it all needs to work together.
Anyway, for what he's doing with, I honestly wouldn't bother messing with the heads. It probably hasn't gotten any cheaper to have heads worked since the last time I checked and it wasn't cheap back then.
I wouldn't run out after 706 heads either. Not that they're bad, as long as they're not CasTech castings ( think those are the ones that were porous and leak coolant), but by the time you went from the 1.89" intake valves to a 2", you could have just picked up some stock 243s. 61.15cc chambers vs 64.45cc isn't going to make much difference. If you REALLY wanted to up the compression even more, you could have the 243s milled. Then you'd definitely need to measure pushrod length, which I suggest even on stock stuff, and you'd have to watch piston to valve clearance a little more closely, depending on cam LSA and duration. I want to say .030 off of a 243 head will take it to around 59ccs. Then you also get in to head gasket thickness to achieve the proper quench. Spark plug gap and hear range selection starts getting important too!
FWIW, my setup makes 317/351 to the rear tires (375/420-ish at the crank). That's through a 5 speed with 4.10s and 37s. I have some 4.56s for it, should it should feel more peppy once I swap them out, but it's certainly no slouch now. It'll flat out move for a 6000lb truck. Stock bottom end LQ4, stock 243s (10.4:1 compression), a ported TBSS intake, 92mm Nick Williams throttle body, 44lb 8.1 marine injectors, and some 1.875" long tubes. The cam is a high lift, short duration. 214/218, .601/.591, on a 108 LSA. It pulls peak torque from like 3800 rpm to 4600 rpm and peak HP is around 5200. Since it carries the torque so long, the HP doesn't fall off very much. I kinda limited myself on cam when I first built it because I was running small tube shorty headers, a stock truck intake, and a stock 87mm throttle body. As it is now, I'm planning to get back up with the cam guy and have another one made for my current setup just for S&Gs to see what it'll do. I'm hoping to get lucky and have it still work with my current PAC 1219 valve springs, but if not, I'll change them out. Other than that, I'm planning on a quick cam swap, some tuning, and then I'll do another dyno run. I'm also going to change from an NGK TR5IX (heat range 5) with a .060" gap to an NGK TR6IX (heat range 6) with a .040" gap. I think I've been hearing some arching going on, but I'll see when I pull the plugs tomorrow.
It ALLLL depends on how much money you want to spend. As does everything in life
TLDR: you can keep it pretty simple/somewhat less expensive and still make good power!
