Joe

I have been doing a little research on this subject and what I have found leads me to believe that you are misunderstanding Reformed Baptist CT. To be sure what you said is correct about Dispensationalism. But it is not true of Baptist CT, in Baptist Covenant Theology Abraham’s promise that the Messiah would come from his blood line is perfectly continuous with the arrival of the Messiah and the fulfillment of the New Covenant.
John Owen speaks of the point that the Abrahamic =Promise of the New Covenant. So says John Owen commenting on Hebrews 8.6,
See the following link under John Owen on the Covenants.
http://members.lycos.co.uk/reformedbaptist/homepage.htm
John Owen of course is a paedobaptist, but he appears to agree with Baptist CT.

Tom