A NACA-Langley photo of a wind tunnel model of a B-58 variant, dated 1957. While generally based on a stock B-58, at least three things are diferent:
1) The wingtips are turned sharply down. Presumably, the wingtips would be like those on the B-70… hinged to be horizontal at low speed, and angled down at high speed to benefit from compression lift.
2) A wider cockpit (on a possibly longer nose), presumably for side-by-side seating. Whether this means additional crew in back is unknown.
3) A smaller external fuel tank, carried under a pylon under the left wing root, rather than on the centerline. It looks like there might be another tank under the right wing root, but it’s hidden behind the fuselage. This would open up the centerline position for either a single very large weapon (a large rocket, perhaps), or another fuel tank/weapons pod. If the latter, the design would seem to indicate much greater range than the standard B-58 could attain.