As Bryan said, the MT open hoppers are very easy to take apart, and reassemble, so that's probably the easiest way to trim the screws. And, since the 1027s fit perfectly, I'd recommend them, rather than trying to install 1015s.
As for where to get flathead screws, I got mine from J I Morris:
http:e//jimorrisco.com/miniature-screws/
If my recollection is correct, the 1027 uses the same couplers as both the 1025 and truck-mounted coupler boxes...
....if so, by the time you buy the flathead screws and remove the couplers and springs from the MTL trucks, all you need are the 1027 coupler boxes.
