You’re funny.
I think the printing press could be something that most of us here could develop with very little help.
Something that would make the greatest impact.
http://www.metmuseum.org/toah/hd/prnt/hd_prnt.htm
Work on paper first. Paper was not widely available, which was the real problem, not the availability of printing tech.
If you had an offset press or laser printer in 1015, you’d have almost nothing to feed it.
The big breakthrough was the idea of movable type and the alloy to make them which had to be hard enough to keep it's shape and soft enough that it did not damage the paper.