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hotwire I guess, did these use the air valve thing fitted to the thermostat housing ? as opposed to the three plug that does

The Aus delivered 4 plug hotwire ones do yes . I think Subaru decided to double up here with the cold air bypass and the ECU's or gauges (can't remember which) temp sensor . What it does do is make removing and refitting the thermostat housing a right royal pain in the ass because the air bypass hoses are awkward to work round/loose .

Typically the Spider manifold uses a two wire Nissan style dumb bell valve which is MUCH easier . If I get time I'll look into the wiring difference to see what Subaru did with the temp sensor on the spider engines (manual in car) . You may be able to use an alternate valve and a plain EA81 thermostat housing it it suits your means . The issues would be finding somewhere that sees engine heat because if the valve body cools down its rotary valve opens . They are a Bi Metalic strip with an electric heater set to warm up and close in the approximate time it takes the engine to lose its innitial "chill" . They stay warm/hot when bolted to the engine so that the valve stays closed with the engine stut down and its electrics powered down .

All part of the fun , cheers A .

Looking at Lturbos post on this thing he has one on his Aus delivered and I am guessing his is 4 plug ECU. My spider has no valve but coulda been modified. These thermostats are tricky things. Tested a nice clean one and it don't open, just like the dirty rusy looking one. A high flow thermostat at 180 may be the shot for summer. Tridon do not reccommend utting a colder thermostat in newer (efi?) engines coz maygive wrong signals to ECU, so they sell a high flow for twice the price.

The bypass air control valve on the spidey is located under the throttle body not on the thermostat housing.

Uh huh. obviously I need to have a closer look !