Measuring directly on the front of my 351W block (which unfortunately is still mounted on my engine stand instead of being a complete motor) the distance you asked for is 10". If it helps any, my 351 RPM intake measures about 5" tall from the front seal lip to the top of the carb pad. Different intakes will have different heights, and 351 intakes are also taller than the same 302 intake so take that into consideration also when comparing these measurements.
"It's not having what you want, it's wanting what you've got!" - Sheryl Crow