I had the Hedman adapters on my D ports and you could run 2" on those, I bought matching stubs and built a set that were 1 7/8 stepped to 2" , they were still a d port header, not round port. I think Darby runs 350+ cfm d ports on his 505 and runs 9.50s. So depends on how fast you want to go. He would have to chime in on his tube size.
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Illinois Outlaw Gassers
6.27@107
9.97@131
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