For spreading the wheels in Flyer trucks I have used this tool from Port Lines Hobby Supply, it is sold to spread the side frames of the Flyer trucks. It has a thumb wheel and gives a fine adjustment that I find helpful to open the gauge of the wheels.
SPREADING-TOOL #2
Similar uses to tool #1 above, but this version allows you to apply pressure slowly, and to "lock" the tips in place once you have spread the sides the desired amount.
$18.95
Ray