I just sold a clifford intake that would fit your 250. I was going to put it on my 194 inline 6 but decided not to. If you use this intake, I believe you have to use Clifford headers as well. OH yeah, in JC Whitney you can order a Offenhauser Intake for a single 4 bbl carb setup that will fit a 250, forget how much $. I think it was around $220 for the intake.

Good luck in building your engine...

Steve