On both models I stripped everything down to individual components.
Renewed small parts like screws, circlips and pins if they were rusty
Washed everything in warm soapy water then dried and left in the airing cupboard for a few days.
De-greased with Isopropyl Alcohol and sprayed with various black paints to give different finish depending on the part being metal or plastic, for example the Stock, hand-guard and pistol grip are more satin than the metal parts. I got a satin finish with a smoother surface on to the barrel compared to the receiver.
I had to do repairs on the solid stock. One of the two was quite badly mashed and held together with black gaffer tape. This one was discarded and replaced with the Magpul stock. I repaired the better of the two which was just split along its top seam. I used epoxy in the split and backed it with a plastic fillet also fixed with epoxy, it is now stronger than ever and the repair is invisible.
As the Classic Army outer barrel is in two parts, the end that fits into the receiver is separate I was able to shorten it to make the CQB version. This joint is held together with grub screws two on top and one under. While it is solid in the vertical plane it does allow for some sideways play so I fixed it with an epoxy and it is now solid.
I did the same with the joint in the 'standard' rifle
Magpul parts were sprayed with Halfords Khaki which I have to say is a lot lighter than I expected but my son likes it.
I am going to replace the Gas Block and foresight on the CQB version with a flip up version and remove the top handle in favour of a Holographic sight and flip up iron sight.
I think I might put a Magpul hand guard on the standard rifle as well, I like them