As Jean indicated, you could leave the original in place in B until after you've imported A so that you have a reference to use for location.
An alternative would be to make a component of the entire A model. Set the component axis to either the global origin or relative to some point perhaps defined by the intersection of two guidelines. If you use guidelines, place corresponding guidelines in the B file. Then delete the model in B, copy (Ctrl+C) the component in A and paste (Ctrl+V) it in B making sure you click on the intersection of the guidelines.
Or, even easier, Select all of model A and copy it (again Ctrl+C). Then, in Model B, click Edit>Paste in Place.