I have read a few post on using the 3800 mustang header on our L67 Motors so here is what I did with mine:

First I used the exhaust gasket to elongate the holes and as Dan stated in his thread you must cut the center flange off, slot the holes and rotate it. I bolted the center flange to the block first then the rest of the header and tacked it up.



I then noticed that one of the tabs on the side of the block was interferring with the header so I ground it off until I had clearence. I may grind a bit more off just for comfort.



To get the collector pointed in the right direction I cut it off at the joint and rotated it ~180 degrees and re-tacked it back together. Now I am coming out in almost the stock location.



From here I am going to make a Y-pipe to bridge the stock L67 header to the Mustang header and bring them together right before it turns to go under the cradle. For the final welding I think that I will have an experience tig welder finsih the job.

Thats awesome, So you are only using one mustang header. Can you get a pic of the l67 header please and is that Oxygen sensor a little difficult to get to?

[This message has been edited by omnivec (edited 05-28-2008).]

They are not a perfect fit but with a little work they work quite well and a lot cheaper then buying headers for the swap. On manual tranny swaps you can use the Mustang manifold on both sides but I prefer to only use one on the firewall side and keep the stock 3800 manifold on the other side with the O2 sensor in the stock location.
The engine will run fine off the one block then if you are worried about the other just add in an air fuel ratio gauge to monitor the other bank. Dan

I dont plan on using the O2 sensor in the mustang header. I just didnt take it out before taking the pics. I am either going to block off the Mustang O2 port and use the L67 O2 or put the O2 downstream in the Y-Pipe. I didnt take a pic of the L67 stock header yet but I can later. It will be a little while before I get the rest of the system finished.