Firestops

[Michael Jones]

"Trying to do 2 pieces, on angled walls, with limited work space, and a 1/4" gap... well, I'm not buidling a watch"

True, and I'm not trying to make it harder for you - that's a lot of mess to clean up, even a thin cut makes everything white for 10 feet.

How about cutting the two pieces you need, then taping 1/4" spacers to the edge of one every couple feet, fastening the OTHER piece in place, then pulling the spacers and caulking?

Or, if you REALLY like messes, mount a dado blade in your circular saw and make one cut... :=)

Yeah that could work.
We're talking about pieces that vary in width from 18" to 9". So even scoring and breaking a piece that narrow is going to be diff.
Now you want me to score and break something HALF that width.

It's going to be messy no matter what.
A friend brought over a shop vac though. That's a GREAT tool to have!