Yes, you can do this. The round Mk1 button caps are a standard part from farnell, and the screw holes should line up just fine The only thing you'd need to do is drill a hole for the knob.
Some people who work at sign shops have done custom-cut faces for the Mk1 panels. I remember seeing pictures, even. I don't have a link to any of the threads handy, though, anyone?
You could go to a local sign shop and see if they'll custom-cut a translucent plastic piece to your specifications. That would work, too.
The only problem is that the sculpted Mk2 handle wouldn't match the faceplate very well.
Personally, I think the Mk2 face looks great, better than any other stereo, and I don't see why anyone would want to change it.
If stealth is your goal, look
here.