Yep have spent hours reading and literally just came to the conclusions if you go holley needs to be all holley. So what are people using for headers if using holley? I cant find any info about their exhaust manifolds that i guess rob power. I will be using the 6.4 and was trying to avoid cutting fire wall, i also want to run the 904 to avoid changing the trans tunnel. Does the tti mounts work with the holley sump?
Maybe some people got the Holley headers early, but I feel like they were discontinued very quickly after their release. I still don't understand the reason because they still have headers for LS platforms of similar year cars.
Check out this thread. He modified mounts and used shorty headers to keep the SRV off the firewall. He's using a 904 as well.
To my knowledge, an center sump pan should work with TTI. I haven't heard of any of them having clearance problems with headers, except maybe some pans with really larger side kick outs. Pay attention to the TTI part numbers since they have a few options based on what steering box you have.