Those notched bores are going to drop the CR also, and it might even be an issue with head gaskets as the fire ring will have to be "outside" of the notches; head gaskets will HAVE to be matched to the modified bores. But, it's a really good start, and if the notches are an issue, you already have another 265 block to swap the rotating assembly into. Like Roothawg said, you'll have less of a CR than you might think with a small bore and stroke engine; probably no more than 10:1 the way it's set up, and with the heads you plan on using. The 461 X heads on my 340 HP 327 short block have pinned studs, and that engine has been in my FED, my 63 Chevy II station wagon, and my truck (where it finally burned a lightened exhaust valve), and one day may wind up in my Delivery. Those heads are also "old school" and are ported/polished on both the intakes and exhaust ports, as well as the chambers being polished, valves polished and lightened (now I have different Manley, tulipped valves in them however). Someone, at sometime, put a lot of time and effort into them, not to mention $$$. Don't worry about the pinned studs, until you have to, and that will probably never happen. You really don't need "big" valve heads on a 265, especially on a streeter, but since you have them, the block is notched for them, and you want to try it, go for it. I'm going to be watching this build closely. I am Butch/56sedandelivery.