Both are now running and fully assembled.
The DD40X now sports Unimate couplers fore and aft, hates 9 3/4" radius curves and looks great on my one wide curve with the roof top blinkies in their full glory. An 80s offering, they're weak in the power department but, have the open walk throughs that they took away in their later offerings.
The Brill trolley suffered from the classic Bachmann malady of the 80s, a weak plastic gear train given to cracking, even when new in the box on the store shelf. I replaced the truck assemblies with later ones that were a drop in fit. It runs great now.
Both were finished with parts offered on their online store. Take advantage of it as certain parts, like the coupler boxes I got the last of, are no longer available.