You probably need screw in shifter bosses, you can probably find them from a frame building parts supplier like Ceeway but otherwise it's something similar to this that you would be looking at getting - http://www.loosescrews.com/Products/shimano-bolt-on-downtube-shift-lever-bosses.html
[edit] cheaper ones here - http://www.cycle-frames.com/bicycle-frame-tubing/NOVA-LEVER-BOSS-KIT-FOR-AL-FRAME.html
@Tychom started
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You probably need screw in shifter bosses, you can probably find them from a frame building parts supplier like Ceeway but otherwise it's something similar to this that you would be looking at getting - http://www.loosescrews.com/Products/shimano-bolt-on-downtube-shift-lever-bosses.html
[edit] cheaper ones here - http://www.cycle-frames.com/bicycle-frame-tubing/NOVA-LEVER-BOSS-KIT-FOR-AL-FRAME.html