OK, straight off I do not have photos of this - you will need to use your imganinations.
I recently purchased a non-large arbour fly reel from a private seller on ebay. Nothing unusual in that.
It's a 4" reel that would most probably have been marketed for Salmon fishing 'back in the day' but I was after it for use as a dapping reel.
The need arose as I sold off a couple of large arbour reels that I had previously used for dapping at the end of last year.
Anyway, I eagerly unwrapped the reel.
"WTF
" thinks I, "that looks a lot like dapping floss being used as backing".
It wasn't.
What it turned out to be was an imaginative conversion of a standard arbour reel into a large arbour reel by applying layers of double sided tape and foam to fill out the spool until a 'large arbour' reel was created
Actually it had actually been done really rather well, I know this as taking the three compacted foam 'rings' and associated tape off the reel took a feckin age.
So there we go folks...... got an old reel you want to turn into a large arbour
You could apply tape and foam layers to achieve the task but personally I'd sell the reel I don't want and buy the one I do.....
H