Well after finding my "precious" I thought I'd take a few pics and give some pointers for those scratching their head on how to install the heaterbox with the jhook.
First off you need to install the jhook into the heaterbox and leave the bolt a bit loose (more than half way loose) so you have enough room to push it back and then up on over the lip, you are doing this at the same time you are putting the studs and heater pipe through the firewall. Once you feel you have the jhook mounted up above, put some downward pressure on the box and tighten the jhook until it's barely touching the underside of the firewall, go and install the bolts on the studs and tighten them till they are hand tight, go back and put a little downward pressure on the heaterbox and tighten the jhook the rest of the way. Then finish up by tightening the bolts on the studs! Wallah! The reason you have to put downward pressure is that if you do not the jhook jumps off the lip and then you start all over again.
Hope that helps!
B