The RD on that bike is a huge-capacity mountain bike model. If when you are in bottom gear your RD pulleys are about the same position as the one in this product photo, you should be fine just swapping the freewheel. In fact you might not even need to adjust anything if you're lucky.
__________________
Genesis 49:16-17
"Well, well!" said Holmes, impatiently. "A good cyclist does not need a high road. The moor is intersected with paths and the moon is at the full."