146cfm rule is theoretical number for frictionless orfice without losses, you can´t use that for cylinder head ports.

350 fps is the limit for local air speed of the fast areas like short side floor or adjacent to pushrod wall, above 350fps you will have losses.

If you calculate air speed for a certain CSA, you will have an average speed for that section, and thats approximately the number you see when you stick a pitot probe in the middle of that section of the port. If average speed of a section is 350 fps, its WAY too fast. Generally anything over 311 fps is not good. It can be higher than that but you need a better port design than small block mopar with std port location and std pushrod location.