tommyboy, did you get it figured out? I recommend making your straps longer than needed and trim later. A couple of mine ended up too short and I had to redo them.
You can find the seat belt material on ebay at very good prices. Heat the ends with a lighter and melt them a bit so they don't fray. I made a jig to bend my pipe and got
a really even rounded curve. I will take a picture and post it in a day or two.