Keith Blacks zero deck 318 pistons can be subed in on the summit kit, there flexable like that. Then see where they sit after a basic bore and hone are done. Then you'll know if the block needs to be decked and how much exactly.
As far as I can remember, all 318 heads are a closed chamber. Remember that later years got a 360 head. If you allready have a set of heads, then just cc them to be sure of what they are and figure out where you stand on the ratio.
Flow rates for the 318 head are very low and are suited for stock and mostly very mild cam upgrades. Porting them is the catch 22 of the OE heads when you have newer iron out there that for about the same cost of rebuilding and porting the head, you can have brand spanking new ones in better shape with better numbers for power. Also, if it is a Magnum stle head, a 1.6 rocker for a more intense cam action.