Hi All, this is a fairly old topic but seems like the best place for me to post some differences between g series and K series gearboxes, I picked up a 5spd from a k12 powered 2008 wagon R for a project.
1st, bellhousing is different, block is much narrower on the K series and starter motor has a narrower bolt pattern.
Overall width is the same for the two alloy casings but the 5th gear cover is slightly slimmer on the K model, also the wagon r K series has the clutch lever arm at the bottom where as most other k series have the clutch arm in the same spot as the g series.
Layout is a little different due to the cable shifter, 1st to 4th gears are exactly the same as cino gears, gti 3rd and 4th are interchangible, high speed hub is the same, low speed hub is the same design but not interchangible due to having more reverse teeth, 3.5 vs 3.2 which is in most g series boxes.
5th gear is slimmer but hub & syncro are the same, 5th shift fork and gear cover are quite different as well.
Both input and countershaft are about 5mm shorter than the g series, input shaft diameter is thicker where the input bearing sits.
No idea why Suzuki messed around with the diff, they have centralised the crownwheel between the diff bearings but this has moved the diff centerline FURTHER away from the center of the car, using a g series lsd is out of the question
Bottom line is there is lots of similarities between the boxes but enough differences just to be painful lol
First two photo's show G box on left and last photo has the K series diff on the left, photo's fixed.