Question: I am especially interested in data input ergonomics: keyboards, mice, and chairs, but would also like to hear about other ergonomic improvements that changed project performance. References to specific research, case studies, or best-practice sheets would be greatly appreciated.

The question is: Do ergonomic keyboards, mice, or chairs make a difference in delivering projects on time, on budget, or according to spec?

Answer: 
I've enjoyed studying this topic of input devices and ergonomics at the Institute of Perception Research in Eindhoven (too bad it no longer exists separately as part of Philips NatLab; it was a cool place to acquire the MSc.).

The question for a project manager can be rephrased as "How do I get more output squeezed out of the team" since all types of actions can be taken. And many pay off already within a reasonable size project. Such as defining a good process, labor instructions, motivation and a good desk.

Productivity is composed of people, tools and processes. And working on each of these three, you can improve throughput by each one considerably.

Back to the question; yes, the choice of input devices can have an impact on direct productivity (number of correct computer interactions per second) as well on indirect productivity (how happy are you with your work).

Regarding environmental factors, there are numerous studies available when you use google scholar to look for "ergonomics" or "information ergonomics". It is not uncommon that a different set up can easily double the direct throughput within the project. Prolonging research on productivity tools can even further raise the productivity. Which is good, otherwise we would all be still hunting mammuts using a wooden stick.

But also please note that for "creative" projects the soft factors can have a much higher influence than the environmental factors. An old book from IBM has interesting numbers. For software engineering (which is my business) I like the books from Microsoft Press which besides normal bla bla on project management include many real-life problems faced within Microsoft. Some titles:

* Software Project Survival Guide
* Code Complete
TL;DR
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This question is only indirectly related to project management, and isn't answerable in the way that you're asking it. In addition, requests for off-site resources or search-engine type questions are always off-topic.

That said, perhaps a valid answer is to simply point out where your question tangentially intersects with Project Management, and where it does not. With that in mind, I offer you the following guidance. 

Applicability to a Project
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While productivity is something that might concern a project manager, ergonomic equipment is more of an HR or facilities issue. The real impact to the project would generally come in the form of:

1. Process issues, such as whether team members can request ergonomic equipment and the procedures for doing so.
2. Budget issues, such as whether such equipment is a cost to the project or to some other organizational unit.

Ergonomics as a Science
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It seems like common sense to say that if you don't have people losing working hours to back pain or carpal tunnel syndrome then you will avoid preventable losses to productivity. If, on the other hand, your question is more along the lines of "How much faster will my programmers type if I get them ergonomic equipment?" then I think you will need to turn to research literature.

Setting aside people's physical comfort and required accommodations, in my experience people on knowledge-based projects spend more time *thinking* than they do typing or mousing around, so my expectation would be that any real productivity improvements will come from the health and happiness of the team members rather than from any measurable improvement in systems input.