If you are going to run high compression then you need all the help you can get with shrt duration cams and cast iron heads.
Shoot for about 180-190 cranking compression and try evans cooluing product NPG-R for coolant. Its expensive but you wont have corrosion to deal with or boiling(375 degree boiling point with no pressure on cooling system.
Evans Cooling 18889902665. As for using 2 exits on back of heads, there really is no need as I have never gotten a Pontiac to run super hot unless it was messed up (as mine was with high compression and short duration cam, rattled like a pig over 3500rpm with 256 duration and 10.5 to 1 heads).