I've had this truck for a few yeas now and I'm looking to step it up and I was wondering if a 6.4 could even fit and if it can what all would I need to do to make the conversion possible? What would I need to change in the truck?

 

Fit yes, all 03+ hemis have the same external dimensions except the hellcat because ya know, blower lol. For starters, this an excellent thing for you because 2005 arguably is the best year for custom tuning. Down side, up to a certain power level you're gonna start wasting RFE's on the regular lol. If you are thinking about the truck or car factory 6.4/392, don't. That is a VVT/possibly MDS engine (with a different tooth count crank wheel) with an active intake manifold. Your PCM can't run it. What you CAN do is take your stock block (or buy a short block all done up) and stroke it. That will net you an awesome torque producing 392 when paired with the right cam. You can either bolt your stock heads back on or get a set (or yours done up) with P&P and/or big valves. Decent set of headers back to your exhaust and custom tune it.