I contacted DPPI about a four gauge a-pillar mount and he contacted the actual company who makes them and here is what they said
“At this time I have nothing in the way of a quad for a 08 Ford SD. Although I have had few requests, it is just unfortunate that there is very little room on the A-pillar for three gauges let alone four. Right now the Ford pillar is not a very popular one at the moment either. To answer your question no the 17-308 is not designed to fit an 08Ford SD. Any questions give me a call.”