Depending on your goals for your truck, I think Sanderson has headers that will fit your appication. These are not long tube equal length units, but they have a choice of tube and collector sizes from 1.5 up to 1.75 tubes and they should be pretty good for a street runner. I am using Sandersons and while they did not have a set that fit exactly, I found a set that was close and we are moving one pipe to get them to fit right. Once we are done I will send them back to be ceramic coated. Sanderson has been excellent to work with, the headers were about $250 in plain steel, and they sent me a whole box of scrap bends and tubes to use while making the mods. Once I am done they say they will coat them for me for $110. Once we are done I will post pictures.
I seem to recall some one posting that they were using an out of the box set from Sanderson in a 60s LS1 truck.
Their web page is
http://www.sandersonheaders.com/. You need to call and get their catalog because all of their LS1 headers are not shown on their web page.
good luck
Pat