This thought experiment reminds me of Mark Twain's novel "A Connecticut Yankee in King Arthur's Court", in which the main character is a 19th-century American man transported back to 6th-century Britain. He used his experience in firearms manufacture to introduce modern weapons and had bicycles constructed for the knights to ride around on. I always thought it was pretty farfetched that he'd be able to recreate such complex technology without the aid of modern tools, much less set up factories to manufacture it in pre-industrial times. But it is a bit fun to imagine someone using knowledge of modern technology to pose as a wizard. As Arthur C Clarke famously said, "Any sufficiently advanced technology is indistinguishable from magic."
Nineteenth century kit wouldn't really be all that difficult to replicate with the materials available in the early middle ages. Even the precision stuff of the time, you can make a surface plate just by scraping an iron sheet. With a surface plate you can make everything else you need. The hard part would be higher quality metallurgy, but it's certainly doable, the Chinese were making cast iron as early as 5th century BCE. Even steel was possible with even Bronze Age equipment.
