Hey guys. I was wondering if someone can help me out?

I want to get some headers, for a better flow and possibly some power.
Now when i look at my truck (87 5.7 v10 silverado) my manifolds seem short!
When I look online at headers. They have long once and than a few short once!
For some of you guys that have installed headers before?

??
If i buy the long once, do i need to redo my exhaust? or just get the shorties???
Any help would be great. thanks