The heads can be swapped out but you will need to lower compression. Throttle body is the same for both 6.1 and 5.7, the manifold is different though. This to can be swapped out but you need to change a few things. Do a search for 6.1L manifold swap, there are some writeups here. A guy on LXF did the same swap (but modified heads not stock heads) and used an SRT8 stock cam and he went from a 14.10 1/4 mile run to a 13.2 from memory.
STROKER 426, 3.4L WHIPPLE BLOWN 300C SRT8 HAS BEEN UNLEASHED!