Set exact pixel dimensions for cropping?

I'm using Final Cut to zoom in on a segment of film. Its a video of a choir concert, and I want to begin with a shot of the entire choir, zoom in on a soloist, and stay on that image for a while. Right now, I have the full choir image cropped the way I want, and the soloist image cropped the way I want, and I have the segment that I would like to be Ken Burns-ed cut and ready to be zoomed.

Is there a way to set the cropping dimensions to be exactly the dimensions on the video segments on either side of the Ken Burns-ed clip? To clarify:

Full image cropped = Top: 104px, Bottom: 48px, L: 218px, R: 53 px

Small image cropped = Top: 483px, Bottom: 75px, L: 266 px, R. 727 px

I want Ken Burns to zoom from the first crop dimensions to the second crop dimension, that match the clips on either side. When I try to do this by clicking and dragging the crop box, it jumps between groups of pixels, so I can never land exactly on the dimensions I want.

Any thoughts out there?