Matthew, can you please just answer my question? I am not trying to fight you. I just want to be clear, are you stating that Horton definitely teaches a "No-Lordship salvation" ("the gospel of justification alone" in your terms)?
No, the Lordship controversy is different again, and Horton is very clear that Christ is Lord and Saviour; he is also very clear that the God who justifies is the God who sanctifies. Regrettably, however, Horton teaches the imperative-indicative division of law and gospel, and thereby undermines the element of "evangelical obedience" which is part and parcel of reformed theology.