turbo 6 bangers post here

Ok, I have a '77 Dodge D100 with a slant six and Im going to turbocharge it. I already bought a turbocharger from an '87 Buick GN that has 30-40k miles on it. It didnt come with the exhaust elbow or the wastegate actuator. I am getting both of them for $54 From someone on TurboBuick forum. The thing is, I know stock boost capability for a stock slant is 10psi, but the stock GN wastegate is set at 14-15psi. How do I get it so the max boost is 10psi with the GN wastegate?