I'd just move the existing extruder on top of the hotend carriage.
You'll probably need to make your own adaptor.

Post some pics of the hotend carriage and the extruder setup.
Then we can see how easy or hard it would be to make an adaptor.

Failing that there are some nice and cheapish all in one extruder/hotend units around at the moment that could probably be fairly easily fitted.

https://www.amazon.co.uk/YOTINO-Asse...572128&sr=8-19
Not the lightweight one I was looking for - but bloody cheap !

Can't find the one I was looking for, I'll ask autowiz - he knows all the new stuff :-) (hell he's bought most of it lol)

Okay reasons a chaep full size nema 17 stepper based direct drive exrtruder is a good diea on an ender 5.

what it won't do.
1) it won't significantly speed things up, but then neither will it slow them down.

What it WILL do:
1) it will create a short and straight path from the extruder to the hotend. This removes the small - but unavoidable - inconstancies that are introduced in even the best optimised bowden tubes
2) it'll make using flexible filaments much easier.
3) it will shorten retraction distances and allow faster movements and shorter wipe distances, which in turn reduced blobbing and stringing.

In other words for about £20 and a bit of printing - it's definitely worth a shot :-)