He's done a very good job on the AD60.
My only comment of anything approaching a criticism would be that I hope the loco won't have to negotiate curves sharper than about 60 inches. He has not put the "dog leg" bend in the sound intensifier tubes where they hang below the footplate at the front. The way he has done it LOOKS better and is prototypical, but they will foul on the leading bogie wheels on any "normal" curves.
Unless he has done built one or joined one in the last few years, AFAIK, Rene does not have a layout nor belong to a club. Thus he can be a little more prototypical. His models are again AFAIK all powered and he did have trouble with a Mashima motor not functioning as well as it should with his NG16 model so replaced it to achieve running fidelity.
A quote from a recent email from Rene that reflects something you said...
"The roughness of the boiler smoothed out with the progressive layers of paint. Base coat, top coat, clear coat, on all I estimate some 20-25 super thin layers. The roughness is barely visible and I wonder if it will be after weathering and final dull coating."
I suspect it will be fine,