Would venture the reason there are no holes for the dt shifters is because your bike had stem shifters w/a bolt-on set of cable stops on the dt. The assembly was like a clamp. You may be better of w/bar-end or stem shifters as you wont have to drill a hole or weld a stop onto the frame, but you
will need a set of stops, regardless.
Make sure your deraileur has enough lateral and forward swing to be able to clear all of the teeth and cogs. For example a 27t der wont clear a 34t cog even if they're both 9 speed. And to avoid 'chaindrop' you may need to mount a 'narrowed' frt der or get one of these:
http://www.paulcomp/chainkeeper.html
Also, you may want to pose your question on the Mechanic's sub-forum as they'll be able to dial you in w/pics! Those guys are the experts and are very generous w/their knowledge.