Engine upgrades

Crate motor. Edelbrock sells one. Many others do also. Pick your performance level.

Keith Craft crate motor or FRPP 5.0 crate motor with a custom FTI cam. Check out keithcrafts econo 331

Oh and put a billet countergear stabilizer and aftermaket shifter on that T5z, both bolt-ons and it'll suddenly be a lot harder to break. under $250 as well

Doesn't sound like you're looking to replace the entire engine. I would look for a balanced package of "add ons". Edelbrock has several performance packages that are balanced for power levels such as:
http://www.edelbrock.com/automotive_new/mc/power_package/power_package_main.shtml

I'm only giving this as an example of a balanced system, there may be other makes that I haven't explored. You would need to add headers and dual exhaust with a cross over to these packages.

But first do a compression test on your engine... need a good foundation before building.

Of course rear gears are the best bang for the buck performance upgrade, but you didn't ask about that.