The ONLY way to know what size chambers any head has is to actually measure the chambers.

I looked at some head info sites. looks like there are several other choices for high compression heads. Lots of guys have used the #17 & #47 heads. Looks like the '68 #15 heads are small valve, small chamber, press-in stud heads, as are '70 #16 heads.

http://ronspontiacpage.com/reference-pages/stockheadspecs.htm

According to the info, the #215 & #216 heads are small chamber, big valve, screw-in stud heads. I have #215 heads on one of my 455 bracket engines. Big valves will require the double cylinder chamfers. I've read that many of the earlier 350 blocks had the chamfers, even if they came with small valve heads. Can't comfirm, one way or the other.

http://www.bassettracing.cz28.com/custom3.html

I'd try to keep the CR down around 9:1, or slightly lower, and run a small Voodoo cam, such as a 256 or even a 262.

http://www.lunatipower.com/Product.aspx?id=1775

Don't know you budget, but for around $500, you can buy some forged AutoTec custom pistons for a 350. These are much lighter and stronger than cast pistons, You can also get 'em with narrow rings, and you can get the pin hole placed where you need it, in order to get near zero deck height, without having to cut any off the decks. The pin height alone will pay for part of the extra cost of the pistons.

For $400, you can buy RPM brand H-beam rods,which are much lighter than cast rods. The lighter, stronger rods/pistons will increase the power of your 350.

http://www.racingpartsmaximum.com/sae4340steelhbeam-2.html

OR, you can buy a stroker assembly, from Butler, and build a really strong 383. Easier to get 350-400hp or more, this way.

http://butlerperformance.com/i-2459...stroker-kit-for-350-block-4-000str.html?
ref=category:1234861

http://www.hotrod.com/articles/hppp-0712-small-bore-pontiac-engine-build/

Yeah, it's not a big problem to make decent power, using a 350 block. Just takes a few bucks more.