Ah forgot one point, I have 40mm carbs with filters (no airbox) 145 Mains, can't remember pilots.
'89 on GSXR list (Hot type) JR10B (STD) JR9B I've always used JR9B's with no issue
Cylinder pressure 1989 on -(std) 170-199
What about advancing the cam timing? It's ok to list the numbers of the cam but if it's not opening the Inlet valve until around 15 BTDC you may be able to open this up 5+.
You might lose bottom end once again but what you lose at bottom you'll gain up top!