Just my 2 cents on this: Undoing the bolts at the heat riser allows each manifold too set better against the head. When the heat riser is tightened up all of the misalignment is taken up at the junction of the heat riser and not at the head. It worked wonders on my 235. I had to remove and replace the exhaust manifold due to some broken bolts. With the manifold apart I could check each piece for true and flat at the head flanges. Intake was good and exhaust was good. When they were bolted together they were not. Kid of a twisted and misaligned if you will. So I put them on while the heat riser bolts were loose. Worked very well. Snugged up the heat riser bolts and nothing moved. Started and was quiet. No more leaks. Drilling and re-tapping holes? Good argument for anti-seize for sure.

Steve H