i think the GA,s use a higher diff (almera/primera)
quote from k11wiki
" The GA16DE has the same bell housing bolt pattern as CG, so can be fitted into K11. 31 series gearboxes retain all the mounting bolt holes for the 30 series gearbox mounts. "
http://k11wiki.com/index.php?title=Gearboxes
you may ? need the inner C/V,s to suit tho 