YES you can send out 4x3 out the composite port. Just go into menu and I believe it's call side mask or something like that. I do this 6 times a year on my webcast. I haven't used timestamp but I know the 4x3 will work.. and you can turn off the OSD, just not sure about timestamp.
When using sidecrop on the HMC, it puts the last digit of the seconds fairly close to the RH margin of the frame when viewed on a typical NTSC TV. That said, most of my stuff is shown via projector as is or used in a video/transcript synchronized display where it's not an issue. Timestamp is found in the Record Setup section of the manual.
Mark, how's the image quality for the composite out on the HMC150? Is is as good as a DVX100? Or close enough that you can't tell the difference when recording to a DVD-Video recorder?