Most modern fly rods can go up/down one line size without too much trouble.
My Orvis spring creek (WF5F) can load a WF4F like a fast action tip rod or a WF6F like a slower "full flex" rod.
Try your 9 weight rod with a 8 and a 10 weight line, see which one loads the best.
There is also different line tapers in the 9 weights, a bass-bug taper might load better than a double taper line.
The bass bug line would be closest profile to the shooting head lines that you are use to.
I would suggest trying that first.
Best of luck.
"Somewhere, over the rainbows. I'll cast my fly...."