all,
While sorting through some of our late father's possessions I was intrigued to notice that a number of "Matchbox" Models of Yesteryear are scaled in the 48th to 50th range and I believe are most suitable for detailing/conversion:

Y-2 1914 Prince Henry Vauxhall - 1:47
Y-6 1913 Cadillac - 1:48
Y-7 1912 Rolls-Royce - 1:48
Y-8 1914 Stutz - 1:48
Y-9 1912 Simplex - 1:48
Y-10 1906 Roll-Royce Silver Ghost - 1:51
Y-11 1912 Packard Landaulet - 1:50
Y-12 1909 Thomas Flyabout - 1:48
Y-14 1911 Maxwell Roadster - 1:49

There are more, just haven't sorted through these yet.
Just thought these maybe of interest to some with an interest in the WWI period and/or diorama possibilities with aircraft etc.

Since they're die-cast metal, they're a real chore for conversions, especially if you want to cut them up. I've ruined a few Xacto saws trying this!

Well all I can say is that maybe if you used the correct tool for the job then conversions wouldn't be such a "chore". Xacto saws are Not designed for that type of work, however an item called a jewelers saw is, and will go through diecast metal like the proverbial "hot knife through butter".