When you say "what's important to replace?" what do you mean? Replace for more power? Replace because they're worn out? What? Be more specific on what you're hoping to accomplish with this car and you'll get better help. Maybe list a specific power number you'd like to reach or quarter mile time or something like that...
It's "just the way you write" huh? So you put unnecessary S's on the end of words thereby making them plural? You're an idiot. An engine with a "V" layout has multiple heads. An inline 4-cylinder does not. If you want help here then be open to corrections and criticism and learn from the more experienced people.
Die please. Kthnxbye.