Howdy
WOW! "1300*,25psi and 4000rpm pretty regularly. The next one will be 30-35psi, should be up around 1500*"
Those are some smoking numbers from a 6.5....
Are you using an intercooler or water injection?
As to your manifold question...Have you thought of using a custom header shop to make your system? I have long tube headers on my blazer made by Headers by Stan. They work great and he was a great guy to work with, seemed very open to just about any kind of custom project.
As a fabricator and gunsmith I know that the cost of any type of custom or low production high grade bolt/stud is VERY expensive. I am surprised that ARP does not have an on shelf item.
Good luck!
1996 Chvy 3500 CCDWLB 6.5 Heathed, NO vac, marine injctrs, ARB bumper, BIG pipe, 3" lift, bright lights, bypass oil system.
1986 Chvy 6.2 M1009 blazer RAM AIR, Headers, Custom interior
2001 Chinook RV, V10 gas
1974 John Deere 1530 diesel tractor
1993 John Deere 455 Diesel lawn mower
1967 GTO, 1989 Honda Transalp
2009 VW Jetta TDI, flashed and piped, 6speed, fun car!
1998 6.5 suburban, stock, daughter's
1993 6.5 3500 CCSWLB GM8, Heathed, big exhaust, gauges, Son's
1984 6.2 ATS turbo 3500, SCDWLB - Son's
3 kids, 1 wife, 1 dog
Gunsmith, Tactics Instructor, Fabricator USMC 87-93 Semper Fi!