i was wondering if i could do anything to modify the performance of my 2005 Taurus SEL.
would a 3.4L V8 SHO fit?

Welcome to the forum!

For the money and frustration you'd have in it, you'd probably be better off to buy a running SHO as a daily driver (or some other car) and keep the 2005 as-is for road trips and the like. Isn't your 2005 still under warranty, which would be voided if you were to install a different engine?

Since the 2005 was never available with the SHO, I think you'd find you need to modify quite a bit, and the computers may not "talk" to one another. I believe 2005 uses a different anti-theft system than the 1999 and newer (SecuriLock versus PATS?).

-Rod

You would probably never pass the emissions tests with a different engine in your car.

Go trade it for a Mustang GT, Taurus' were built to run "as is".