Something similar to Buran but based on Saturn V.
A fully reusable system was not possible in the 70's.
Get ride of the ET and SSME and use an expendable rocket instead.
As it is expendable, try to build it as cheap as possible, using Truax pressure-fed booster as first stage.
The orbiter itself would become a 40-tons lifting body with a load of 12 tons only. This won't please USAF of course, but you'll avoid a compromised design at least.
Btw get ride of the crew and send it separately into a Big gemini or Apollo capsule. Once in orbit unload the shuttle cargo bay putting the "canadarm" onto the space station, not on the shuttle itself.
If USAF really want a spaceplane, best option would be the Black Colt / Pathfinder option, build from existing technology.
Back to topic, I just agree on the fact that an accident was due to happen sooner or later. Just look at the rate of (cancelled) missions on Astronautix... way too much for such a flawed design!