Carmine- a few things. The '57 265 block is a good one.It had thicker walls because they used the same block casting on 283's, so it was thick enough to accept the .125"overbore. The crank is a small journal steel unit. Don't use 265 rods-they were too skinny and broke at the big end.Use the '65-67 small journal 327 rod. it had a bigger beam section and extra mass around the big end around the rod bolts. The 57 block didn't have an oil metering notch in the rear cam journal, I know that '55 265's did, but definitely by '57, that had been changed for the good. Also, the four barrel carbs on the 265 and the 283, even on some of the stick shift 348's were Carter WCFB's. The dual four barrel cars probably all had the dual point distributor with the older style clip on cap and no vacuum advance. Those are out there, just don't get nailed spending too much for one. I have one I'd sell pretty reasonably that checked out to be from a '55 265 Corvette engine. It would need disassembly, cleaning up, and new points, rotor, and cap. They were a pretty good distributor,especially for back then. They look neat,as well.
You had a question on deck height. Deck height is the distance between the top of the piston at TDC(top dead center) and the deck of the block. That can be as much as .040-.060". That much plus the head gasket thickness can really change an engine's mechanical compression ratio. Decking the block is when a machine shop resurfaces the block in an attempt to make it flat, and to get rid of excessive deck height. A zero deck block, let's say, has the top of the piston flush with the deck of the block at TDC. Now, a problem with that, is that at 6000-7000 RPM, an OEM rod will actually stretch about .028-.030" and the piston actually starts coming up higher than the top of the block. A zero deck short block requires-actually demands- a head gasket about .032-.035" thick. OEM steel shim gaskets were a lot thinner than that. If you are going to use them, you need a minimum of .020" deck height after all else has been done to the short block.
Cylinder heads-if you use the '64 327 head, it's either a head ending in casting number 896 or 520. They are identical, I've even seen both number heads on the same engine, but they have a different valve cover bolt pattern than the 55-59 heads. The older script valve covers with the embossed CHEVROLET on them won't fit the later head. Script valve covers off a '60-67 283 would be the right valve cover for this application, they are probably not hard to find. Just don't try to put the early covers on the late heads or vicea-versa.
Also, the 265 and the 57 283 blocks had no side engine mount provisions lika all the '58 on up blocks had, You can't put a 265 in a later car than a '57 Chevy because of the lack of side mounts. If you're putting this engine in a '55-56 or '57 Chevy,no problem.
When you get your short block built and your heads back from being surfaced, then you torque down your heads for final assembly, set up your intake side gaskets, let the gasket cement dry, then manually set the intake in place and check your intake bolt hole alignment. If the bolt holes are off, take the intake down to the machine shop and have him surface about .030" off both sides, the front and the rear. That will get all those holes in the right place, but you might need a distributor spacer to keep from bottoming out the distributor before it's snug on the intake.
That camshaft, the 097 Duntov was also called the "30-30 Duntov" because it was a mechanical lifter cam, and the proper valve lash was .030" Intake and .030" exhaust. The engine will have a very noticeable valve lash noise that went with the whole package. 409's had that same lash noise with factory camshafts as well.
This sounds like a fun project. Like anything, take your time, ask all necessary questions along the way,and do it right the first time.