It can be done, but it will take alot of skill in knowing how to build a car.
there are a couple of ways of doing it , build a full tube chassis then cut floor out of car and build a new floor around the tube chassis like a PRO stock , or strip body down to bare nothing, then build a 2x4 steel frame through stock floor boards, and building brackets to bolt to body to frame.
Might take a look at how guys connect the front sub frame to the rest of the body on camaros, to get the idea of how its done.

These cars are usually done on a JIG to keep everything square, a car that isnt built square , is
a scarry thing when launced with any type of horse power, ask some of these guys that actually have some nicely built drag cars here. Its not a matter of welding in some strong steel and bolting in a rear end , tranny and motor !

I always wanted to build my wifes GEO storm into a pro street car many years ago when she had it , been a cool little turd with a blown 90.deg V6 . To much work , and didnt have a hydrolic tubing bender.

Wasnt it Kugel Komponents that built that V8 Focus? I may be wrong though.
Spray