You assert that the Westminster divines did not teach this doctrine, yet I cannot find in the Confession where they have denied it. At most, they appear to be silent on the Gospel's affect on the reprobate.
Here is what I found of relevance to the subject:
. . . Neither are any other redeemed by Christ, effectually called, justified, adopted, sanctified, and saved, but the elect only (3:6).
The rest of mankind God was pleased, according to the unsearchable counsel of His own will, whereby He extendeth or withholdeth mercy, as He pleaseth, for the glory of His sovereign power over His creatures, to pass by; and to ordain them to dishonour and wrath, for their sin, to the praise of His glorious justice (3:7).
All those whom God hath predestinated unto life, and those only, He is pleased in His appointed and accepted time effectually to call, by His Word and Spirit (10:1 emphasis mine).
Others, not elected, although they may be called by the ministry of the Word (cf. Matt. 22:14), and may have some common operations of the Spirit, yet they never truly come unto Christ, and therefore cannot be saved . . . (10:4).
And I will again make it clear that I never denied the Gospel is preached to the reprobate. I never denied that our duty to preach the Gospel should conflict with the secret counsel of God's election. As God's elect are secret and hidden from us until such time that he should reveal them, we are not to deny the Gospel message to anyone and to spread it without prejudice. This is what is meant by "although they may be called by the ministry of the Word." As Jesus said in Matt 22:14,
For many are called, but few are chosen (AV).
All are called to believe on the name of Jesus Christ and be saved
outwardly; yet, this not being an effectual call, has no authenticity for those who would not hear the Word. Even more, as dead men have no ears to hear and the inability by which to choose, they could, nonetheless, never perceive and receive that message. And unless God desired their repentance, he would not genuinely offer them such, for God is pleased that they should suffer in and for their sins.
Soli Deo Gloria
Jon