Apologize ahead of time for vagueness, but I recall someone here getting one in the past week or two and commenting that they fit small, I think they said they should have sized up one.
I google searched the forum ("site:styleforum.net junya sizing varsity"), these are from the top two results:
There's measurements on a closed B&S for a Medium: P2P - 20", sleeves - 26"
Another B&S size L is stated best for a 48 or slim 50.
Seems to confirm what I remember. Best of...