Hi, I'm using the stock exhaust manifolds, my engine is from a Soarer/SC400 and the manifolds fit with no problems, but the LS400 manifolds are a different shape and foul the bellhousing.
For the engine mounts I just used some steel box section which I bolted to the 1UZ, then bolted the OEM Mitsubishi rubbers to the other side of the box.
The rear sump doesn't fit straight on with no issues, it needs notching out on both sides.
I'm using a stock 4M41 clutch setup, the torque figure of the 1UZ isn't actually much higher than the peak figure of the 3.2 Di-D so the gearbox should hold up fine. I haven't actually driven it anywhere yet apart from around the block as it's currently having the exhaust made.