How much should I expect to pay for internals so that I can bump my 07 GT above the 450whp mark and not blow it?

 

For the money of internals and to have a shop (I will assume you wont be doing this yourself) pull and rebuild may be almost as much as a new block and internals. I paid 4500 for mine and its rated to over 900 horses. Alot can depend on the shop doing the work, I know i saved a bundle on all my work because of the shop I use and all the buisness my car cleb has gotten them in the past.