Heres what I have:  1971 Dodge Dart Swinger with a 318 engine and a 904 transmission, with the 8 3/4 rearend. 

I already have a 360 motor that I am planning to put into the car in the near future. Aside from a different engine mount and torque converter, is there anything else that I need to do this swap?  I am planning to use the 904 trans that I already have.

Thank You--Ryan

the 360 is not balanced to the 904 trans., it will vibrate  

Yeah, that's about it ryan.  Keep in mind though, if the 360 you have already has spool type motor mounts or the older pad style like your 71 already has.  You might be chasing more than just the one mount, as you already know the 360 has a different mounting pattern on one side.

Also, you might want to consider using headers if you don't already have them, 318 manifolds aren't much in the way of making power.  Installing headers on an A body is a challenge.

Make sure you KNOW for sure that the converter you get is offset balanced for a 360.  If  you are dealing with a local trans. shop you would be surprised how little some of these guys know about mopar stuff.  I learned the hard way on the converter.  After telling the shop to give me one for a 360 when I did my swap they gave me a 318 one anyway and the car shook like hell.  If you this happens to you, it will be very obvious what has happened!!!!!!!!!!  I ended buying a balance kit from mopar which was still available at the time and had them welded on to my stock 318 converter to make it right.  The kit comes with a template to show weight placement.

Your 904 trans should work just fine, I have the heavy duty 360 style one (A999) which has a couple extra clutch plates and a wider low reverse band.  A 318 trans should be plenty tough for a mild 360 though.

Instead of finding a converter to match your new power train you can use a B&M flex plate that will bolt directly to your 360.
These flex plates are balanced according to the engine and are a simple fix for external balance motors.
They work great and are SFI approved for your dodge.