Hard to tell from the picture but a closed end wrench may not clear the dimple in the pipe. If not then you might try a line wrench for tightening brake line and fuel lines. To give it more grip on the bolt if it feels like it's not gripping the head tight enough, I sometime clamp vice grips across the wrench to keep the jaws from spreading under pressure. I would look for some smaller head, 12-pont header bolts. I used ARP bolts. These are 6-point but I thought I found 12-point. Will have to look at my car.
https://www.jegs.com/i/ARP/070/100-1...QaAm93EALw_wcB
Seems like there were two lengths available and I used the longer one due to the combined thickness of the header flange and copper gasket.