Future man in space/shuttle replacement vehicles

"Ben Hallert" wrote

Hence, the Shuttle Derived Launch Vehicles, one of which is a
heavy lifter that would throw Saturn V class payloads.

Read more he
http://en.wikipedia.org/wiki/SDLV

Seems a lot of engineering would have to be done to the shuttle's main fuel
tank, to use it as a heavy lifter. The thrust of the shuttle engines are
applied to the mounts on the side of the tank, and the proposed lifter has
them on the bottom end of the tank.

Also, you would need to stage, and get rid of the main tank, (my guess, not
anything I read) so you would need some more engines on the second stage,
and more tankage, right?

I do like the idea, but I'm not so sure it would not be easier to start with
a clean piece of paper, except for a few things like engines, and solid
boosters. Come to think of it, the solid boosters have had their problems
too, right?
--
Jim in NC