Is the fan working at all, or is it only blowing air on one setting?
My temp lever doesn't move right accross either, but that's because I didn't adjust the cable properly when I put the aircon stuff back in.
Physically the st185 components might fit under the dash, but then you'd have to modify the ducts so they line up with the vents. I think the real problem would be the wiring, not really worth the hassle if its just the core or fan that needs replacing.