Mechanical Questionnaire Sierra

I Have a 1992 Gmc Sierra 1500. With a 5.7 V8 350 In It!
No Extended Cap But with a long box. 8 feet!
Just a few questions which may sound stupid to many but I need to find out somewhere before I take it to a mechanic!
Just Started to rake in the money so lets start

First I'm taking It In For A Tune Up (sparks, filters, distributor cap, etc.)
That's Not A Problem But As For Extras Such As
Manifold, Cam, Headers, Pistons Whats Yay And Wats Nay?
Should I Get The Engine Rebuilt Before Hand?
Or Just Go For A Brand New Engine?
Any Tricks I Should Know Or Anything Helpful That Could Well.. Help?

Thanks For Any Help
It's Hitting 240 km.. But Haven't Had A Problem.
Replaced Much On It but Engine Work Is Needed!