its always mildly amazing and a bit frustrating, how complex the simple routing of a few header primary pipes can become once you need to snake them around suspension and roll cage components in a tight engine compartment, especially if your trying to maintain a semi similar length on each tube, but you look like you've done a good job, and your sure to have gained experience that will prove very useful in the future.
every time I build custom headers I get a bit better at it, gain a bit more skill with a welder, a good deal more skill at cutting tubing and measuring angles, accurately, and usually swear Ill, never do it again, but theres a great deal of satisfaction in doing the job correctly and you'll be surprised at the difference well designed headers can make in your torque curve.
the result seems to be that you constantly feel that the last set you built could be improved upon and in almost every case thats not only correct but you see how, you could have done so, yourself after you've finished each set, so, you look at each set as less than ideal, but the truth is that after a few sets you gain enough basic skill that the gains you make at first are very noticeable, but as you progress , and gain skill in both the planing and fabrication, stages you produce better and better headers, and making major improvements becomes a bit harder to do.
keep in mind most factory headers are designed with ease of fabrication, and low cost and easy installation as the primary goals.
no header will function well unless matched to a low restriction exhaust behind it! and theres a very significant difference in the power potential between your average commercial header thats randomly matched to a cam, and having selected both the header and cam to work together as a complementary matching pair in a selected rpm range, where the combination fully exploits cylinder scavenging efficiency,gains in excess of 40 hp are common.
header primary length, diameter and collector design are all something that can be fairly accurately calculated, if you know the engines displacement, compression and cylinder head flow and cam timing.
viewtopic.php?f=56&t=352
viewtopic.php?f=56&t=1166
http://www.slowgt.com/Calc2.htm#Header
http://www.bgsoflex.com/auto.html
these threads might help
http://metalgeek.com/static/cope.pcgi
http://www.pontiacracing.net/js_header_length1.htm