An oil catch can is designed to 'catch' the blow by off of the two top nipples on the cam covers (they then run into the throttle body and accordian hose of the turbo, or the equivilant of that in your case)
The blow by generally cause power robbing carbon deposits into the intake manifold and oil buildup in the intercooler and piping (for turbo cars of course) You should also see some benefits from this in your NA supra.
To instal a catch can, it must be mounted under the hood on the cold side of the engine (intake side, the can must have an air filter on top of it to better help the oil vapors to condense into the can) The oil vapors must cool down to condense into oil, thus it should be mounted on the cold side (I've seen some mounted where the battery was and by the brake booster and clutch master cylinder). I would Tee the two nipples on the valve cover into one line and run it back to the catch can inlet. The outlet line should run to wherever the stock lines went to on your NA supra (for turbos this is the accordian hose) I would also cap off the vacume line that was conected to the stock lines on the throttle body.
Viola! A working catch can! Just make sure to check on it every now and then to empty it.
The catch can does not separate particulates and sludge/impuriies from the oil, that's the oil filter, the catch can 'catches' most of the oil vapors and any impurities associated in the vapors. I hope this helps you out
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