Did the Austin/Morris 1500 have a B series engine?
The MG1100/1300 were very similiar to the Mini bud had a wider wheelbase,
therefore different subframes and axle shafts and longer lower control arms,
the two 1100's I saw (one MG and one Austin) had disc brakes in the front and
1/4" wider drums in the rear, and hydroelastic suspension. The MG1100 has a
very good flowing head and dual carbs (1 1/4"), so it makes a good doner for
a wimpy Mini (what I did with mine).
I don't believe Leyland (MG/Austin?) made a 5 speed gearbox.