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I notice with my Mast 305 heads and a 3/8" pushrod the intake side is very close to the side of the hole in the head but it does not seem to touch maybe like .005 clearance though it's full travel cycle is that the norm on LS7's in general? Exhaust side is fairly centered just the intake is offset all cylinders and you can look down the hole to the lifter and see the offset.
Wow, those are big heads! You are getting into Big Block Chevy head territory.
If it even rubs slightly, you need to clearance the heads. If you can slide a .005" feeler gauge through, then you should be okay (I would prefer .025" because of heat expansion and defelction). Make sure you check them through the entire travel.
I'm running Manton 3/8" x .145 rods so I don't think they are going to flex much at all but they seem consistent though the travel it may be a tad more I just eyed it and put some lube on them.