I know the grip length is the same (or is it?), but is the length? Can one put a Commander Slide on a standard frame? Can anyone enlighten me?

With some modifications yes. Maybe Tuner will jump in, to give you more concrete answers.

Rgds

__________________
John Caradimas SV1CEC
The M1911 Pistols Organization
http://www.m1911.org

The length of the grip is the same on the Government and Commander models. You can put a Commander top end on a Government model, but you may run into some problems. First, the dust cover on the Government frame is longer than the Commander's. Second, the frame rails and recoil spring guide rod abutment are cut back 0.100" on the Commander frame to allow the slide a little more travel distance. On a Government frame, this 1/10" can create some ejection problems. I tried sticking a Commander top on a Government frame and ran into the ejection problem.