Dominic,
You may already know this, but sassafras are not the easiest of tree to transplant. Now is a good time to be digging and planting them if you are going to, but you still may have a large failure rate. Trees larger than seedlings are going to be especially hard to keep living. Sassafras trees from the nursery are generally pot grown in air-root-pruning containers. That gives them a large advantage over field grown stock. Non-air-root-pruned container-grown plants are very likely to have root problems later on. Field dug stock are less likely to make it through the first summer.

Come to NE Texas and I will give you all you can dig!!!!!