503_EF9

well im very frustrated at this point,
ive picked up two "b series" clutches from two of my good freinds and both of them are the same size but will not fit on my transmissions mainshaft. they look like the right clutch bolted up to the block and the pressure plate fits perfect...

im not to good with transmissions, but this is starting to make me believe i have the wrong transmission?
engine is an ls and the transmission i was told is a gsr, theres no stickers vins or identification on the tranny i dont think, but i know what a b series hydro tranny looks like and i know thats what it is.
any help would be appreciated this is whats keeping my engine from going in.
i dont care if i have to get a new clutch or anything but the last thing im trying to do is order another wrong clutch...