Another one of the main fabrication hurdles with the swap (but one of the easiest and funnest!) is routing the coolant system lines. Luckily, the input & output of the water system is on the exhaust side of the engine.
Instead of trying to find rubber hose of the exact shape, I purchased some 1-1/4″ 0D 6061 Aluminum pipe from a local supplier for the straight runs. It was cheap and very easy to work with.
The engine-radiator line was easy to fabricate. If you notice closely I reused a line from the 16V engine as well as one from the 20V clip.
The radiator-engine line was more complicated since I needed to incorporate the filler neck. Also, I am not using the stock MR2 oil cooler, so I don’t need to route the line over the exhaust manifold. (if you do use the oil cooler, just mount the filler neck over the manifold.) I ran the line over to the driver’s side of the car, straight up to near the fuse box and then back over into the thermostat housing. For the elbows I just purchased 2 proper sized hoses that each had two 90 degree bends. Then just made up some brackets to hold the pipe to the firewall. I attached the filler neck to the firewall as well.
The heater core lines are a lot easier since you just use flexible rubber hose. I forget the diameter I used, but it’s the same as the 16V lines. I used the same bracket that was on the tranny to hold the lines in place. You can sorta make them out in the below pic: