NGM, let me clarify (my perception)--I may not have a direct "replacement" for your exercise.
It is my opinion that the majority of the skeletal muscles of the body serve one purpose: to assist the bones involved in whatever articulation is necessary.
So, in essence, if the pullover directly causes the contractions of the pectoralis major, latissimus dorsi, serratus anterior, and the longhead of the triceps-- I would probably try to find other ways to contract these muscles efficiently and moreover, sufficiently.
I do not believe in muscle "shaping"- I believe that the shape, insertion, and origin of a muscle is general, but also specific to your genetic structure. You are either going to 1) contract the muscles, or 2) not contract the muscles. The question is: How many fibers will contract?
Taking this perspective, I suppose my logical answer would state that you would have to find other exercises that either worked these muscles that you are concerned about either synergistically, or worked the muscles in some form of "isolation" (which I also do not believe is 100% possible)--all muscles work in synergy with other muscles. I believe that when the larger (and more popular) muscle groups are worked together, you get what some call 'compound' exercises.
The question then arises: What exercises would work the pecs, lats, serratus and triceps? Maybe none in the same synergistic fashion as the pullover, but there are many that would work them sufficiently using a different plan of attack. I do not for one second believe that a pullover is a 'standout' exercise.
Therein lies my answer. Sorry if I misled you. I am more concerned about you not injuring yourself just because you believe this is the ONLY effective exercise to intensly contract and stretch these particular muscles- for whatever reason (this is where my "butterfly" analogy came in)
I am entirely confident that Pumpster could give an even more in depth answer to what exercises would be sufficient (and why)
Again, this is only my opinion. I try and use logic and science when I work a muscle. That seems to get me from point A to B "as the crow flies"...
Good luck my friend!
