2003 Dodge ram 1500

Yes, a Hemi 5.7 will fit. The problem is there is a large amount of work required when you replace a different size engine in a vehicle. Motor mounts, exhaust system, transmission, emissions, gauges, wiring, etc. All of this needs to be figured out. If you are paying a garage to figure all this out, it will be a very expensive endeavor.

I would recommend spending the $4,000 - $6,000 to buy a newer truck with the engine you want vs. trying to upgrade your current truck.