robbsracingengines

So I bought this Mustang that is making a loud rapping noise in the engine. It sounded like it was coming from the passenger side under the timing cover. I took the cover off and the chain on the passenger side was super loose. I decided to replace the chain and guides. The noise didn't go away. It must be a problem with the rotating assembly. Normally I would just take engine out and rebuild it. However when I took the cam covers off to do the timing chain job I noticed that there is 2 different heads on this engine. One has bridged cam caps and one doesnt. It appears one head has been replaced and with a non pi romeo head. My engine is a windsor. I have a bad case of OCD so I have to move on from this engine. I've looked around some local junkyards for an engine but surprisingly there's not many Mustang engines. There's tons of GM and CV engines though. So I'm thinking I want to buy one of those. I figure they are probably well cared for low mileage engines out of grandpas car instead of some thrashed Mustang. That's what leads me to my questions. Some say they are 100% the same from a long block stand point as a Mustang. Others say that's not the case they have different cams etc etc. Does anyone know for sure? And what about the years? I know 2001 or newer on the GM or CV engine so it will be a PI engine but how new can I go? There's a yard nearby that has a CV engine out of a 2010 CV with low mileage for a decent price. Can you use one that new? Same hp? What about the intake and injectors same?