I have a Loar LH 300 archtop acoustic guitar and am going to put a pickguard on it. The basic brackets are listed either for thick or thin body guitars. The brackets for thick guitars have a longer arm.

Anyone know whether I need a bracket for a thick or thin guitar?
I think the differance between the two is wheather there's one or two screws holding it to the body, one screw for thin bodies, two for thicker ones. You can go with the long one for your guitar.