Re: spacecraft design
You have to consider the fuel tank and the shuttle itself as one item at launch. Given that you want the expensive engines back, they need to be connected to the lander. You also want the sources of drag (e.g. the wings and tail) as far back as possible.
Given that the engines are used in the launch, and the whole point is to make as much of it usable as possible, you don't want the entire thing on top of a first stage that is disposed of each time you launch.
The only viable place to put any booster rockets is on the side, like the side boosters of the falcon heavy or any other boosters used on any rocket in the past.
The only alternative design I can really think of would be to mount the fuel tank right on top of the shuttle - in front of the nose.
Of course that would mean that you would require long pipes to get the fuel to the engines, instead of a direct connection.
I don't think there is really another alternative layout for a reusable rocket launched winged craft, unless you were to put a smaller winged pod on top of something like the Falcon Heavy or the BFR where you can land the first stage as well.
At this point though, a good capsule like the Dragon is going to work out cheaper and lighter, which is why of course that's the route SpaceX is taking.
The Shuttle was, as much as anything a product of the technical limitations of the time, as much as it was the technical abilities and the political wrangling that went on.