I had an ol' army jeep and I found to match style/size of the stencils it's far easier to print & cut yer own if yer familiar with Photoshop/Paint/any editor.
Oh and BTW - while there might
have been a standard, IRL few if any of the motor pools used the exact same stencils (vintage anyway)... I doubt the poor grunts cared lol So use w/e font you think looks right
"If it moves salute it - if it's still paint it" o_O
A few pics to help ya out;
1942 willys army jeep pics - Google Images
An interesting problem is matching the shade
of OD to be period-correct lol but the "hunting camo" green found in most hardware stores is pretty close to WWII OD.
Nice project too BTW