The first problem you will run into with a frame for a scamp
is that it isn't a standard straight frame. The frame makes dips for the floor area at the door. A custom frame to fit the existing frame thus giving you a lift as well as supporting an older "weak" frame might be the way to go. Otherwise you might consider taking the body off, and then having a newer frame made to fit the dimensions of the old one. By the time you get to considering replacing the frame all together your already in the realm of unlimited possibilities in my opinion.
Whatever way you chose to go about your project, please take lots of pictures, and keep us informed.