al, that's the T25 '86 on exhaust primary setup, very expensive, even today's replacements supplied are good quality tho, and hard to improve on power wise, made for mid range in a heavy T25... the early type 'stat housing is integral to the pump by the no 4 exhaust stub unfortunately, the late pump is more efficient, that's why V.W changed it, again, '86 on and injection models, gives a full cross flow coolant path for cooler running, you can then use a remote 'stat junction pipe housing,
hope that helps... regards..