You might get away with that for visual work, confined, but for photography its very unlikely it will be stable enough. If you want to do photography then the safest bet is to work with only 40 - 60% of mount capacity. But with such long tubes you have the additional problem of "lever arm movement" a type of mount flexure that is caused by the leverage action a long scope has on the Dec juntion of the mount head
This link might give you an idea of what you're looking for.
http://members.iinet.net.au/~rog1/as...hy_mounts.html and Roger is only trying to mount two small refractors. From only my brief experience with astrophotography I would suggest to start with small scopes. Either Telephoto lenses on a camera or a short tube refractor. The longer your focal length the more demanding it is on your mount and the harder it is to get a successful image, especially with a mediocre mount. You can do a lot with a smaller good quality mount using shorter focal length scopes