"Works" is a relative word here. It probably will work but it will not work well.
Have you considered, you already have a tele advantage fo 640mm with that lens. Maybe the only place where a EF, or full frame, lens has an advantage is on a crop body. 640mm is going to be a challenge to deal with. Nearly 900mm is really tough. Strong tripod. Everything has to be right for the shots to be worthwhile.
EB
EOS 1D, EOS 1D MK IIn, EOS 1D MK III, EOS 1Ds MK III, EOS 1D MK IV and EOS 1DX and many lenses.
