I really like your idea. I'm behind it 100%, and I'd like to have a built up 307 myself, for the same reasons as you. Cool!!! I'll drink to that.
I can help a little bit with your questions. I am running 305HO heads on my 355. It makes 375-400 horses all day long. They are 601 castings.
I know that the 305HO heads are great for a 307 build up. The 305 vortec heads are supposed to be pretty good too. Standard 062 or 906 (350cid truck engine) vortec heads might not be such a good idea, they would kill your compression ratio.
Your best bet is with a set of 305HO heads...casting 601 or 801. Some guys prefer the 416. In some places they are called the poor mans racing head. They are proven on smaller engines like 283s, 305s and 307s. A friend of mine, the guy that ported my heads, only builds 350s with 305HO heads. He has been around a long time, and has done all sorts of parts comparison testing. Those heads are VERY capable castings. There are a lot of myths about them, and a good portion of them aren't true. That is why they appeal to me, and likely do to you as well. Stock parts that GO, and when tweaked, GO faster.
They have small chambers to make the compression ratio such that you can run a hotter cam, and in even small-valve stock form, will perform very well on a smalled cubed sbc. They have 155 cc intake runners, and a decent chamber shape. You can make decent power with them...for a price that literally cannot be beaten...anywhere.
A 307 is 3.875 bore x 3.25 stroke. A 327 is 4.000 bore x 3.25 stroke. A 350 is 4.000 bore x 3.48 stroke.
If I were you, I wouldn't worry about turning it into anything but a 307 with some grunt. A torquey cam, intake/carb, some 305HO heads, headers and exhaust...equals instant smile.