In frame cam change?

I have a 71 Dart, 318 2 bbl, i want to put a 4bbl on and want to put in a mild cam just to better suit the intake, I was also thinking of putting the 302 heads on that I have lying around (I think my valve seals are gone in the engine in the car, lots of blue smoke at start-up but not when running) just for something to do over the winter. The problem is I dont have the space to pull the engine, so I am wondering if the cam can be changed with the engine in frame and what it takes to complete the job in the easiest way. If anyone has tried this it would be helpful if you could give me a short step by step list of what you did. If it is to much of a hassle I will leave well enough alone until I complete my other engine, about 3 yrs away...