never touched a surf. but engine wise, they're based on the hilux/4runer. so if it's not on the exhaust manifold, for toy trucks, it's usually on the exhaust down pipe. just b4 the cat. I4 & V6. easy job.
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now this is for the hilux/4runner. not surf specific. but the surf, engine wise, should be the same.
I4,
http://www.ncttora.com/fsm/1990-1995...e/descript.pdf
V6,
http://www.ncttora.com/fsm/1990-1995...e/descript.pdf