04 3.9 Mustang rebuild, need help.

[04SN95mustang]

I have an 04 3.9 mustang I'm wanting to make 500wbhp out my stang would it be best to rebuild the 3.9 with 240 000 miles or get a new 3.8/3.9 or just go for a 4.2 ?

 

[atermate]

Any news on the rebuild?