Ok, from the leaflet I have in front of me, the Canon mount is not one of thise that need special instructions, so here goes.
Attaching the mount to the lens:
A. Be sure to set the aperture ring of the lens to the maximum aperture.
B. Align the green dot on the base of the lens with the green dot on the adaptall-2 mount
c. Press the mount downward and turn clockwise until the mount is locked into place (while turning, the silver release button will slowly depress and then will open and click when the mount locks into position)
D. Slide the coupling key of the mount (tab that David speaks of) into the matching slot of the lens aperture ring. Sometimes the coupling key will slide into the matching slot after step C and therefore this step may not be necessary.
NOTE: some mounts have 2 coupling keys. If the custom mount you own has 2 coupling keys, be sure to engage the 2 keys onto matching slots on the lens aperture ring.
It can now be fitted to the camera.
Hope this solves the problem, and you may like to know there is a website dedicated to the Tamron lenses, although the mount part isn't posted yet.
http://www.adaptall-2.com/