440 motor mounts

I plan on using Schumacher mounts in my small block to 440 conversion in my 72 dart swinger. My question is, what would using the stock c body mounts out of either a 66 new Yorker or 71 imperial cause for problems? Basically why cant I use these mounts? Kind of thinking about just going front motor plate instead of mounts, I just want to make sure I can get the engine in the correct place before welding up a set of elephant ears in the wrong spot. Also since I'm sure its a no go on the mounts, would it be possible to throw the engine and trans in the car, mount the tanny down and use one or the other mount to figure position and then fab up elephant ears