The main problem is that conversion of Loran time differences to latitude/longitude is not terrible accurate, depends on ground conductivity, etc. Expect errors of several hundred yards. If the Loran receiver is still available, they suggest a "local correction" technique. Of course, if it is still available, you can just use it to go to the coordinates.
If you are taking Loran coordinates from a chart, simply use the latitude and longitude scales along the edges of the chart and use those in your GPS.