those are a great looking set of pipes !
a couple of things i do on any set of headers i install, i "stole" from our passed member, Mr. P-body [R.I.P.]
i cut the end pipes from the middle two at the mounting flange, and drill one mounting hole on each flange segment two drill sizes larger.
these simple mods dramatically increase the sealing ability of the flange, no matter how thick the flange is. this is especially true of the 1/4" and 5/16" flanges.
doing this can seal any flange of any header to any head.
i also use studs in the head, along with reduced head size flange nuts.
doing these simple things has worked superbly for me over many years and many header installs.
just my personal experience.
your mileage will vary.
