aluminium head questions

I'm not sure how far in the hole the pistons are. That's the 1st thing I'll check when I pull the heads.

You're right about the 311 heads. I'm going to go w/ the 524 now. I'll send them to Modern.

I've already purchased a Cloyes hex-adjust double roller timing set w/ a thrust bearing and cam button. I also ordered a bronze gear.

As for a cam, I think I'm going to go for the next step up from the one I have listed:
Comp XR286HR... 236/242 duration, .580/.570 lift w/ 1.6 rockers

My current cam is a 230/236 duration w/ the same lobe separation as the one above. It has .521/.524 lift w/ 1.6 rockers. It idles great (750 rpm easily) w/o much of a big cam lobe to it. I want to go to the roller for the added lift now that I'll be able to flow more air. I figured I'd bump up the duration a little too to get more of a lobe to the idle. The lift is almost the same b/w the 230/236 and 236/242 roller cams. Will I gain much by the added duration or would I be better off w/ the lower duration to increase dynamic CR (my static probably won't be over 10.0)?