Whats your budget? A build on some motors can be easier then others. If I was you personally a mild build wouldent involve pistons. If I was you I would go with the JG Engine Dynamic Redline Series head it comes with:

swirl polish stock valves
Ti retainers
comp valve springs
comp valve job
full port and polish

For 700 bucks
300 core charge

Run a cheap but gain worthy kamikaze header, intake, and exhaust and you got a mild build. That head is a complete head by the way, so its basically bolt on, although you do have to pay extra for assembly. Im sure the shop would charge you for installing it. A couple of hundred bucks for tuneing it to im guessing. Might want to upgrade your fuel system.

They will also regrind your cam with the specs of 402/390 (lift in / ex) for 120 bucks

They also do milling and extra assembly's pistons and more. But that is your mild build right there. It really depends how much you want to spend, if you wanted to go full retainers and springs you would upgrade to the pro-series. HP isnt cheap and not a walk in the park unless it comes stock.

Jon