Jim, The lens length is 300mm, so why go to 1/450. The rules of this is 1/mm. The crop factor is only a comparison between a crop sensor and a ff sensor.....a 300mm on a crop sensor is like a 450 on a ff...or another way to put it, to take a shot with a ff 450mm and crop it down. A 300mm designed for a crop sensor is 300mm, and a 300mm on a ff is 300mm.
Am I all wet?
Think you got it backwards above. A 300 on a FF is like a 450 on a 1.5x crop; 480 on a 1.6x crop.
And yes, use 1/(LensMM*CropFactor) with CropFactor=1 for FF.