I used round pipe and just reshaped the lower plenum. With a good carbide bit (get this at a tool supply store) and lubrication (keep the bit lubed and stuff wont get stuck in it and it will eat the aluminum like crazy) you can do it in 5 minutes if you do a good job marking off where you need to cut.
I do think its cool to use all new upper plenum pipe. Then you can determine the diameter of the upper runners and maybe taper down @ the lower for velocity blah blah blah
I still think everyone goes too small on the surge tank and a bit to long on the runners. I guess the corner of the valve cover gets in the way so some configuratios fit better then others.