I am about half-way through building this. Mostly, it's pretty nice. I have run into a snag though. The pivots for the Carpet rocket-launcher appear to be in about the right place, as does the launcher end of the hydraulic elevation ram - however, I discovered, possibly too late, that the end where it fastens to the vehicle is in the wrong place, so that the only orientation you can mount the launcher is with rockets vertical... Unless, of course, I've done something horribly wrong.
Oh, and the chains are slightly too short if you make them the length they suggest - I found I needed one more link to make it fit right. The roller assembly is fiddly enough, without the chains being too short!