The E58s also didn't have much compression. Yes, maintaining the flow and picking up compression will help but first, I'd put a cam in it. Low compression with stock cam is FAR more disappointing than low compression with a reasonable cam like the 340's. I'll take a stout cam with 7.8:1 everyday over a stock 318 cam with 10:1 with irons.
Far as I know- all that 273/318 stuff's supposed to come in right at 62 and anything else's been worked. 69cc is right around what I've seen for 587s yet that were stock. I don't think there's optimized with the parts you have on hand. The only thing that'd really be a worthwhile upgrade over the 587s is Magnums and if you're really that worried about compression, you should grab the whole long block that has the higher CR pistons than the early teens.