Tranny swap -4 spd to a 5 speed?

I have an 87 Excel 'L', with the 4 speed manual tranny. Since the car is ready for a new clutch anyway, I would like to know if I can possibly swap the 4 speed for a 5 speed tranny....hopefully just changing the shift knob, but keeping the same axle shafts, clutch cable, etc. It would be nice to get top miles/gallon on the open road.
Any advice?

I thought I would bump my question back up to have a little visibility. I want to get a 5 speed tranny for my 87 Excel, in place of its 4 speed tranny. Does anyone know the tech details about this?