how hard it is and what is involved in the installation of a lift kit for 84 gl wagon

Depends on the lift used.

On a basic look at it...

 

Unbolt the rear torsion bar, gearbox crossmember, engine crossmember and raise the car up, fit blocks in with new bolts. Unbolt the front struts at the top and install strut lift blocks and rebolt. Un bolt the steering uni joint and install steering extension. Maybe radiator pipes need replacing with different ones. maybe brake line extensions need installing. Maybe shifter and 4WD shifter brackets need modifiying, replacing with ones that come with the kit?

 

I'm sure I've missed a bit. But thats all the big stuff.