In conjunction with head/cam install, I am trying to determine the correct pushrod length.

Heads - '04 LS6 stock heads (no milling)
Head gaskets - aftermarket .040
Cam - 238/240 dur, .590 I&E lift, 112 + 2 LSA
Lifters - Comp Cams type R lifters
Rockers - Comp Cams shaft mounted, 1.7 ratio

From what I can determine, I shouldn't have to deviate too far from stock length, if at all.

I know I will have to determine the exact length when I finally get it all bolted together, but am sure several other have similar experiences.

 

I dont know your cam's base circle but it is like .06 smaller and thus .030 smaller on the radius. That makes the pushrod length need to be longer. The use of .040 gaskets makes it come back the other direction by about .014". The net rod with the exact same preload would be near 7.416".

Using the Comp R's is the issue here. Since they are only recommended for use with less than 1/2 a turn on the preload, there is no way to be sure your pushrods will work since they have to be torqued town to 22ft lbs and have no adjustment. If you had adjustable rockers this wouldnt be an issue.

Since the huge cam you are using is going to need the pistons notched I would mill the heads while they are off to get your compression up more. I wouldnt use those lifters.

Most of that cam's awesome potential is going to be wasted without a set of heads. Its a 500rwhp set-up with decent heads.

What tuning are you using? Your profile says you have a 2005 and if so that is good since the 05 is easy for the type of tune you need. My HPtuners cable is also licensed for all 2005 and I would love to help you tune it. Big cams are a big challenge. I can tune it. The challenge is the level of driveability.
Think about it and get back to me in a PM.