The phrase "a large and difficult" is correct and usable in written English.
It can be used to describe something that is both significant in size or extent and challenging in nature.
Example: "The project we are undertaking is a large and difficult task that will require extensive resources and time."
Alternatives: "a substantial and challenging" or "a significant and complex".
It is a large and difficult work, an experimental and visionary interpretation of the famous legend.
The VRA offered one small solution to a large and difficult issue.
In addition to having a large and difficult site to contend with, the developers face several obstructions in connecting that site to the downtown.
Since Inca mythology covers a large and difficult terrain, local cults developed in many places, utilizing the same characters in different incidents.
But it was a formidable challenge he had set for himself, playing a large and difficult body of works probably never intended to be presented whole, on relatively unfamiliar instruments, and understandably, he seemed a bit daunted at the start.
Whether he was offering advice to Colonel Ba, in a self-consciously humble, soft-spoken manner, or moving from task to task with his characteristic rapid, almost bounding gait, he displayed unflagging energy and almost unclouded high spirits, not unlike an eager camp councillor managing a large and difficult but highly successful jamboree.
"The journalists have to sell everything, so they present each thing like we're really on the verge of a quantum computer - but it's just another step in what is a large and very difficult research effort.
Kinsella and Pence described it as one of many species of Capillaria, a large and taxonomically difficult genus.
We were able to achieve participation from a large and extremely difficult study population and implemented the Multidisciplinary Integrated Care model in a single care organization having the possibility of uniform implementation.
It was just a temporary problem, yet it pointed to a larger and more difficult issue facing the company: how to decide whether a song is, in fact, authorized for copying.
