Al I have seen your 40 and 41 here before. I also have a Bachmann 40. If you converted your to battery you could probably run them together more easily. Plus if you bought another Bachmann C-19 you would have the wrong tender for 41.
Now to the head light. That was one of my favorite things i had to scratch build. i made it out of a slice of PVC conduit. Its 1-1/16" OD, witch turns out to be 21 scale inches, 1 inch larger than the real head light. The number boards are off of the original Accucraft head light but i carefully cut then in half and removed some material to shorten the length of them. I made the shade from sheet styrene, there is also some flat trim around the from and a strip of half round. Glued to the front is a piece of brass that I rolled into a circle and soldered together. The reflector is a stock mini mag light reflector witch fits perfectly inside the conduit. Oddly the mag light reflector is exactly the same scale dimensions as 41s real reflector, both the diameter and depth. Thank you mag light. I also used the Mag light lens. Once assembled the light has two holes drilled into the bottom and mounts to the stock accucraft bracket with the stock screws.
Here is a photo of it nearly finished.
(http://i81.photobucket.com/albums/j220/jeffsparrow/lil4114-1.jpg)
Now if you have a 1:20.3 scale ruler you can use these specs for the real light to build your own. 41s headlight is the same size and type that 346 has currently, as well as other locos through out the years.
(http://i81.photobucket.com/albums/j220/jeffsparrow/41headlight.jpg)