Are the selector rod's on a S1 and S2 gearbox's different sizes?Changing my box and this is all thats left to go on but i cant get it on!

Its as if my linkage(S2) isnt wide enough to go over the new selector rod

So im now wondering if its an S1 box and i need the linkage to match?Or even a diesel one..?
I know the box has been opened and i can see it has a LSD
ANY help appreciated!
Thanks,
Stuart