So I am trying to break in my freshly rebuilt 312. I have fired it off twice now, but have shut it down early due to the #1 & #3 cylinders getting hotter than the others. The #2 & #4 are not getting hot at all. #5,#6, #7 & #8 on other side seem pretty evenly distributed. The exhaust header is glowing red within a minute on 1 & 3. I assumed a vacuum leak after the first time. I replaced the intake gaskets and checked for flatness etc. while doing it. I am running a 3x2 edelbrock with Stromberg 97's. I have the front and back blocked off for this break-in so I am pretty confident that there is no vacuum leak there. After replacing the gaskets there wasn't any change other than the #4 cylinder seemed to liven up. #1 & #3 still hot and #2 not. Just to clarify when I say "hot", I am using an IR thermometer pointing at the header pipe 3-4 inches out of the head. I am getting avg. 300 deg on LH Side and 450-500+ on the #1 and especially the #3. This is with just a couple minutes of running at 2K rpm. I am afraid that I'm not doing the cam any favors by not running it in properly, but at the same time I don't want to cause more problems by running it in for 20+ minutes like it is. Any suggestions?