Right - time for an update. Firstly getting a tempered glass replacement is easy - we have at least one company making kitchen splashbacks etc. Total cost was AUD650 and about half of that was for painting the black margin. No screen heater wires but that's not a problem up here in the tropics. Here is the template I cut out (no guarantee it will work for you, of course.)Were you able to get replacement glass made for your Gren?
Next - consult the online Grenadier manual for the installation procedure - wouldn't that be nice? So, in the absence of the manual, this is what our local windscreen man did. Firstly, take off the lower half of the internal trim. You will find the windscreen wiper motor is secured through two holes in the glass, and the windscreen washer hose in the third. Disconnect those. This fixing arrangement is great because you can fit them with the glass on the bench. Then it's a matter of simply gluing the pane (with motor etc.) into place. I drew the pane a millimetre or two small (just in case I got the template wrong) and the two fixing holes for the motor slightly large for the same reason. Glue the pane into place, and you're good to go.
NOTE! The internal trim is screwed into the motor housing - meaning that you have to replace the internal trim BEFORE gluing so you can be sure the pane is exactly aligned. It would probably help if you used an extra long bolt so you can start the alignment before the glass touches the glue.
Hope this is some help to you all...