I think it would be hard to find a 449 c.i. 915 production headed BBM at 2450# with a single carb and a relativly sm solid lifter cam [.560 lift],that will go faster than 149mph. I must mention I built this motor for a street car that I no longer own, so I stuck it in the racecar. 155mph would be 8.60 range and that would be dificult with any production cyl head N/A. With the proper evac system, ring pack and cyl wall finish there may never be a problem. But I have seen many good running strong BBM motors push the pan up and split it and still run for years. Seen shop towels or pig mat packed between intake and pan to absorb the oil. Street cars would be even more prone to crankcase presure problems as pan evacs don't work with muffs. Indy and Koffels make there valley covers from material 10X thicker, [Koffels] and 20X thicker, Indy. Both obviously were addressing the valley pan issues when they designed the valley covers for there heads. The stock valley pans are weaker than you think.