how do i determine what size gearbox i have ?

i have a 1994 115 evinrude. it currently revs to 6500 with 4 people onboard. i'm trying to buy a higher pitch prop but no-one seems to be able to tell me how to tell if i have the 6cyl or 4 cyl gearbox on my model. the model no. is E115TLERC. the serial no. is o? 0 3317357. i've tried asking elsewhere and either i'm asking the wrong way or i'm getting answers from idiots, so i'll include this info . i already know it's a 4 cyl . i know what pitch prop i need, and i know they came out with either the 4 or 6 cyl gearbox.