I've always followed the "good 'n tight" method when tightening header bolts. The bolts toward the firewall and near the accessory brackets would probably be close to impossible to get a torque wrench on, so I've never bothered trying and just got them as tight as I could.
I've had great results starting with the center bolts and working my way to the outer bolts using the good and tight method as mentioned above, then retightening them every couple of days for a week after the install. My bolts stay tight and I haven't had to touch them for over two years now.
Nobody can accurately tell you how tight ................
Tight Is
OR
That is too ... Tight or Loose
At long distance and over these pooter screens
Its kinda like finding zero lash .............
Its a show me thing
BUT
Your basic objective is to ...................
Compress the gasket a bit
and
That amount is sufficient
Some go too far beyond that point and do thread damage
Very easy to do on Aluminum Heads I might add
Some believe ... more tight is necessary cause they've lost bolts
thus
They then get involved with the above issues
Bottom line on header bolts is ... in most cases
If you put em in without some locking method .........
It is almost a certain bet ... They will back out
btw ... I've used simple lock washers for decades with success
and
If you run Aluminum Heads ..........
I'd not do thread locker liquid as the material is easily damaged
I did mine yesterday and i could only get the torque wrench on a few so I got the feel for it on a torqued one and tightened the rest by feel. I did it to 30ft lbs
manual states working from the center to the ends ,tighten the header bolts to 26-32 ft.lbs. and then tighten the exhaust flange bolts evenly to 20-30 ft.lbs.