Greetings from a fellow 7740/740 owner. There is a power take off point at the back end of the motor armature, as you would know. According to the instruction manuals it can be used for drilling or routing.
The issue is it needs a chuck with an odd mounting fitting that hasn't been produced since 1970 or thereabouts. I have been looking for bits in US and Oz for more than ten years and never seen one of these chucks listed anywhere but the DeWalt/B&D Accessory catalogue.
A second is the speed of the take off, being direct drive off the armature, it runs around 2800 RPM in 50Hz countries or 3300 RPM in 60Hz countries, so is generally way too slow for router bits and way to fast for medium to large drilling. Some contemporary brands of RAS had a power takeoff that was geared up from the armature and could get to about 10KRPM, but again the adaptor is a very rare accessory. Other saws used a faster universal motor geared down to drive the the blade, and had a faster direct drive PTO.
I have seen articles where people have mounted a mid size (1000-1200W) router on an outrigger attached to the motor housing so it can be set to do compound (mitre + bevel) work. Can't recall whether this was on a 7740 or a contemporary rival but it can be done.