I have an 89 5.7 block 40 over with flat pistons. I'm going with 906 vortec heads and the vortec TPI manifoild. nothing has machined as far as the heads.

I have no idea as to what to get for a cam. nor do i really know what I'm looking at when it comes to cams.

I want a smooth idle.
also will i need to change the push rods to a different length because of the heads?

 

Cam choice will be limited without something done to the heads.

What will you be doing with the car when it's put back together?

Push rod length is dictated primarily by the type of lifter - roller or flat tappet. If you're building an engine to the nth, have shaved the heads or block, or use some unusual combo that requires custom length push rods, that's when you start worrying about push rod length.