Altered the original plan only enough to accommodate the materials I had lying around without going to buy more lumber. The workbench I built is not as wide being only 48" instead of the 55" noted in the plans. For the top of the workbench and the lower shelf I used 1x4 furring boards again, because it is what I had for material at the time of building.
Once I made the basic frame, I squared it and then installed the supports for the table top and the lower shelf. Once the supports were in I cut the 1x4's to the appropriate length. As I laid each respective board, I also laid a good dose of wood glue down and then clamped them in place. I let those boards set with glue for about 5 minutes before going back and using a 2" brad nailer to finish them off. Once the nailing was done, I removed the clamps and moved to the next series of boards. Because I had several clamps I was able to lay about three boards at a time and let the glue set for another 10-15 minutes. Working slowly and methodically got the whole job done in a couple of days of a few hours a piece before completion.
Easy project and something that will last a long time when done correctly.