A "frame swap" could also be called a "Money swap", "Time swap", or "work swap". It will swap money spent from one thing to another, time spent from one thing to another, and work spent from one thing to another. But it saves you NO money, NO time and NO work, PERIOD.
Modify the original frame with the MANY kits out there to do this and you will be money, time and work ahead. And when you are done you will have a 1949 Dodge truck instead of a 2000 Dodge truck with some other body screwed to it.