Stupid question but are all the 4.6 engines compatible with each other? Like would a engine from a 07 fit a 05?

 

All the 05-10 short blocks are the same. The only differences are:

1. 08-10 engines have updated spark plugs and different coils.

2. 09-10 engines have intake manifold with integrated charge motion control valves. Earlier ones had a separate CMCV assembly.

3. 09-10 engines have updated and more reliable Denso alternator.

4. 07-10 engines have different water crossover at front of intake manifold with integrated thermostat housing, and less radiator hoses.

 

Would I be able to put a 07 engine into a 05 mustang without having to modify anything?

 

so would I be able to swap a 07 v8 into a 05. There's a one out a 2007 near me with 50k miles and comes with tranny and everything on the engine. Would I need to modify anything to put in in?

 

It'll drop straight in. If the engine's fully dressed, just remove the water crossover from the 07 and swap the one from your 05.
It's a good opportunity to upgrade the stock exhaust manifolds to headers if you can fit them into your budget. They're easy to do while the engine's out. You might also want to replace the engine mounts with new OEM units if yours are 15 years old. Again, it's easy to do while the engine's out, and you can clean the engine bay to have it looking smart for the replacement engine (which you can also clean before it goes in).
I'd advise you to replace all coolant/heater hoses and the drivebelt as preventive maintenance (especially the heater hose assembly under the intake manifold) as these would be a PITA to do later on.