Yes, it is possible to mount an Atlas/Rivarossi 0-8-0 shell on an N scale Spectrum 2-8-0 mechanism. While it is not a Boston & Albany class G6e Consolidation nor a Class H10A Mikado, the engine does look hefty enough to tackle the Berkshire Hills beyond Chester, Mass.
While my efforts are far from complete, a good place to start is to read the article by Michael Wong about installing a TCS M1 decoder on the TCS website. I didn’t read far enough and ran into some trouble that I’ll describe at another time.
My initial concern was to remove the large hemispherical housing for the headlight. You can see where I cut it off. After a lot of scrapping to open up the boiler cavity, I found that I had to cut off the air compressor because it would interfere with the eccentric crank as well as cutting off a square appliance located in front of the air tank since both of these were molded into the boiler cavity.
Right now it appears that since the mechanism is such a tight fit, the boiler shell will not need to be mechanically attached to the mechanism.
I've been unable to attach photos of the boiler shell and mechanism on this site; however, I've done so on other sites.