Well the Grunge isn't for everyone as it's a sand bed loaded with live things. It's part of the Garf way of setting up a tank and yes it does work. It doesn't elminate the cycle but it does speed it up. The thing is you need to have a sand bed, which a lot of people don't want to have now. I think Ronen actually set his tank up that way.
Adding the water from the 30gal isn't doing much but if the tank is fine, low nitrates, then it doesn't hurt to use it.
On the LR he said he had 50lbs and it's been in the tank for 3 years. It's possible he could have little or no die off from just the short move. The think is there maybe some things growing on the rock, like sponges, that will die once they're removed from the water. So you don't really know until you move it and see. Some people setup tanks and use LR that is fully cured, that has been in some one else tank for a long time, and they never see any spike or cycle at all. In a tank that size if he has a small cycle, from the LR, it should be that big of a problem.
Your right on the bio-load being to much for that size tank and he is going to need much more LR than the 50lbs he has. That also why he really needs to get the 50lbs into the tank in the beginning. The aragocrete rock and Grunch will help make up the rest.
What is suppose to happen is that the aragocrete rock will absorb the bacteria from the Grunge and become LR. This will become his bacteria, along with the other LR, that will support his tank. So what he should really do is move the LR, from the 30gal, into the tank with the aragocrete rock and grunch and place the corals in a bucket, or maybe give them to some one, and then check his tank after a couple of days and see if the tank is ok. At that point he can start to add the corals back.