Yea mate got the 4JG2T, have a geez at these ones https://www.onlineautoparts.com.au/products/Set-of-4-Glow-Plug-Bosch/ZPN-36764 not sure whether you’ll be able to get them in the states but they’re the ones I’ve put in and they work like a charm.
It fits over the wheel wheels! And you're right, the storage "box" is slightly above the height of the folded down back seats. There's metal brackets on the leafs and it all just fits enough that it's snug and doesn't move around when set up.
I have a sketch with some measurements written on it that I'll dig up for you. Mattress I got from Amazon, wood is just 3/4th inch Furniture wood from Home Depot.
Works great, I've driven a 500 miles with it permanently in the back and haven't had any problem with movement or shifting. Also is a good way to organize the trunk.