F100 counter rotated drive

[outragesteve]

I have a pair 0f 2002 F100's, 20" shafts, on my Whaler. I would like to convert one drive to a left hand unit. Can I take a new F115 counter drive, replace the 25" shaft with a 20" shaft and be good to go? Or, is the f115 drive gear case a larger diameter than the F100 gear case. Thanks

[boats.net]

Comparing the 2 in parts book it don't look like they interchange. The F100 lower unit will interchange with F75,F80, and F90.