I have a Eurosport TI motor in a 78 frame
I believe the GL motor is TI too?
they will fit but they are are longer so you'll have to move the expansion bottle
and decide which rad and thermostat system to use.
You'll also need TI spark units and coils plus sections of the GL ignition harness
and enough knowledge of the few but important differences of both systems not to make any serious cock ups.
It isnt difficult as long as you have the parts and know what you're doing