I wanted to try making my own 3-1 merge collectors, I have to say once you have a good jig they are very easy.
I welded up a piece of angle iron into a 90 degree square, welded another tube to that with a nut welded to hold the 13 degree elbow used for the merge collectors
all that i had to do once the jig was set up was to rotate the tube 30 degrees one way and then 30 degrees the other way for a total 60 degree cut.
3 pipes finished ready to weld
tack welded collector
and finished with a small transition on the end it expanded from 2" to 2.5"
so i made one more of those and was ready to move on to the actual headers