Genuine Bully should take 1/2" springs (~.500".)
Make sure you don't use the clone/copy springs as they are considerably longer.
Also, don't just go by the spring relaxed oal. Check what they measure in a spring tester at installed height - that's what matters.
We go through a lot of effort/time to match springs on our Intercomp spring tester when we service clutches.
They do things so much differently than I am used to from my 2 cycle days regarding 4 cycle clutches. The only time we ever measured spring height was when we 1st put the clutch together. Just a starting point! After that, we would adjust the clutch stall RPM, at the track, to the peak torque RPM (from dyno testing) of the engine. But that was the dark ages!