How to test 5.7 hemi?

Pull the oil pan and valve covers and look for where the damage occurred to start and then go from there. The most common things I have seen in failed Hemi's (from reading forums) has been either a dropped valve/valve seat or a broken rod for whatever reason.

That engine you have looks like an older truck engine since its has the metal covers and older style coil, those early engines (03) had a few valve spring issues on the exhaust side.

Just an fyi with the wiring harness stuff, if you find a used computer hotwireauto will tune it for you for 250 (in my case he did it more cheaply since I had wiring done)

If you run a manual transmission you can get away with a more simple wiring harness and it probably wouldn't be that terrible to create from an old truck harness. If I hadn't found the deal I did on my harness I would have gone that route.