Those look nice. Theyre almost identical to what we have on Shane's TFS car, which are also 1 5/8th. The big problem with this style header, and this will be irrelevant to you because of your setup, is that you cant get any of the 3.5 downpipes to clear where the crossover joins up. Thats why we scrapped the design.
We're currently building some 1 3/4 headers that I think are going to be the hot ticket.
I wish the demand was there.. I really would like to do a production run of the big tube stuff. I know it works but the masses want someone else to be the first guy to try it and everyone is waiting on everyone else.