Use Hooker slip-on reducers, 2" to 2 1/2". Pictured here at the top of the photo (no flange)....
http://www.jegs.com/p/Hooker/744791/10002/-1

Some motors took the temp off the head, some off the manifold at the very front. Here is a photo I found showing the outlets at the front of the manifold and also a threaded bung on the thermostat housing where you could mount a sender, but I would only do that as a last resort. By the way, I didn't draw the yellow arrows, they were already on the pic.
http://i243.photobucket.com/albums/f...1/IMG_0288.jpg