I just bought a 93 phazer for my kids and it has a polaris 1.75x136 track on it and the previous owner tells me it is heavier than a series 4 151. I would like to stick to a 136 and I may start hackin paddles off this track. This should be a great project sled.
I think AC made a 1.5" x 141" Attack 20. I know you said 136"x1.75" or 2", but I would think a big wheel kit or something would take up the excess and it would probably be the lightest track you will find, by far.