sarp foo'
1) yes the head choice will affect the bottom end work in the piston selection. You have to chose the pistons to suit the head. Going a single in my opinion is better because u have only half the amount of items needed to be purcahsed, saving both money AND weight. Depends what HP u want to get out of the motor, will determine what turbo you need. (also factors like cam selection and headwork will affect that too)
2) Apparantly gtrgeoff is using a 25 pfc with his 26/30 conversion in his gtst, so best to give him a pm and find the details (i think its just a coupe of sensors need to be changed)