Echigoya of Japan has done us a good service with this DIY Guide in having a TM M4A1 CQB-R Shoot and Recoil AEG into an M16A3... "Black Hawk Down fans out there. Here is a simple DIY guide on how to convert your Tokyo Marui Sopmod/CQB-R to M16A3. Note: During the convertion you will need some tools and basic machining skills, if you don't have a lathe and milling machine a dremel tool and alike will also do the job."
The video below shows the complete conversion. To go the DIY area, click here.