So my last adventure was to make adapters to transition from Chevy 250/292 intake port to GMC 270/302 port. It turned out good but I was adapting a Weber DCOE triple carb intake and the Weber carbs are about $500.00 US each so I am looking for a more reasonable , cost effective(cheap) route to follow. I looked at old pics of GMC manifolds and McGurk was a popular manifold of the day. The McGurk manifold has runners that are separate from the "log" so I thought I could attempt that. I found that plastic plumbing elbows are roughly the shape and size I wanted so I started with that. I made some flanges with MDF and made a core mold from plumbing pipe. The castings turned out OK but I'm getting what look like pinholes and pimples on the exterior of the castings. I was thinking I was having a gassing problem but when I sand down the castings the pock marks go away. So I think I'm having a sand issue , not a gas bubble issue. Maybe a more experienced metal caster will chime in. Anyway, I got three useable castings for the runners and now I have to make a pattern for a "log" and top.