Delete all the faces of the frame or body whichever you don't need or one then the other to save both as separate models. Don't forget to delete unused verts and save under a new name.
Press the space bar to highlight the first face then click the 'Follow Current Face' icon
. Hold down the space bar to cycle through all the faces quickly. The faces will be ordered in two sequential groups, first the body then the frame or vise versa. By cycling through the faces determine which is the first of the portion you want to delete, lets say it's the frame. Once on the first frame face hold down the Ctrl key then the Delete key until all the frame faces are gone... be careful to stop before you get to any body faces... if you do delete some body faces by accident just close the model without saving and open and try again. Once you've succesfully deleted all the frame faces go to the Vertex menu and click the Delete All Unused option and save the model under a new name.
Now select all the vertices by holding down the Alt key and pressing A. With all the verts selected go to the Groups menu and click on Vertex Groups, give the group a name then click Save Current then close the box and save the model again. You will open that saved group to center/translate the body model onto it's new frame when the time comes.
Repeat the above to save a desired frame.
To ressemble, open up the body model then go to the Insert menu, click on the Model option and select your new frame. Save the new assembly with a New name.
Tip, do your face mapping before assembly to make life easier. Save often, there is no undo option.
That's a quick and dirty 'how to'. I'll elaborate if you need more help, just ask.