Engine swap in a 2005 v6 mustang?
Without makign your costs extreme, I would just go with the transmission from a Mustang GT, same with the rear and axles. Your modifications are gonna be probably engine mounts (Although with Ford's modular engine, you may not need different mounts. Would suggest them thoguh for the more powerful motor.) You will need to change the coolant system, namely the radiator (The old one may not fit with the V8) as well as some other parts when switching from an automatic to a manual, including adding a shift linkage, etc. Have fun!