Airwaves still lists the conversion on its website:
www.airwaves.org.uk/acatalog/Online_Catalogue_1_72_Scale_Conversions_14.html
but for the expense and the work involved, you'd be better off waiting for AMtech who plans on revising the AMT/Ertl B-52H kit with new nacelles, updated antennas, new pylons with new bomb racks and (I think) JDAM bombs. I expect you will see the kit out early to middle 2004 for around $50.