it seems a very good project. In your schematic there are several mismatches respect to the original project.The transistor Q2 is a PNP, not a NPN, I’ve uploaded the transistors library bjtdibox.lib to add in
..LTCLTspiceIVlibsub directory. Inside there are spice models of BC550C and the PNP BC560C.
I’ve added a directive to include the library in the new .asc file.The DI-box project use a 5:1 transformer,
this ratio normally refers to turns and then voltages ratio, not to inductances ratio, and in your schematic are reversed. If the turns ratio is 5:1 the inductances ratio must be 25:1, for example L1=250H and L2=10H.
Now you should be on the right track, let us know about your results and if you like share them with the community.