Mitch, the brake lines are 26 GA wire and the fuel line is 24 GA. Both come from the jewelry/beading section of stores. The 24 was Walmart. the other one may have been Michaels.
As far as the black, this was my inspiration, and you are right, there is a bit of black shoeing on the inside.
This will be continued here: http://www.modelcarsmag.com/forums/topic/97646-background-diorama-flatheads-to-boxers-engine-rebuilders/?page=6#comment-1618176