I'm doing a 20b with a g50-52. I'd love to see another.
Fran has the dimensions of the 20b rear side housing to make an adapter in-house...providing he has the dimensions of the Mendy box.
You will have to go dry-sump, as the engine sits between the frame rails, not above them. No room underneath for a wet sump to hang down below the car with only 4-1/2" ground clearance. I have made engine mounts that bolt to the topside of tabs protruding from the side of my 3/4" sump plate and parallel 2x2 frame rails. The engine is 1/8" above the bottom of the frame. Can't get any lower really. It looks like the engine belongs in there, unlike those LS lumps.
Not sure what turbo you have but if you have the stock twins, throw them in the garbage. I have a GT4202r which is about the largest (frame wise) turbo you could fit in the car. You may be able to fit a GT45 or larger if you relocated one of the 2x2 diagonal aluminum tubes, but turbos of that size really belong on drag cars and dyno queens unless you want a one-mile runner.
I finally just ordered a Water-to-Air (W2A) intercooler system. You will in all likelihood need to do the same. This has been a huge challenge and expense to (hopefully) engineer correctly. I have planned for the exchanger to mount horizontally above the tranny and behind the upper crossbars. You will need the street tail for this, no way around it. My IC will mount in front of and above the engine. Custom spec'ed unit, as is the heat exchanger.
It could be possible to run an Air-to-Air (A2A) system if you plan on not running too much power and mount the IC where I will mount my heat exchanger. There are two side ducts, which I have enlarged, but I am running dual oil coolers behind those, so no room for A2A IC. You should know the importance of oil cooling for rotaries and understand you will need those in place.
The fuel tank as delivered will not work. The outlet for the shifter cables and any wiring you have going through there will come out right at the main pulley. The hole/tunnel through the tank that allows this will have to be angled left, right, or above depending on how you run things.