Taken from "Matchbox" From 1953 to 1969, 1-75 Series Regular Wheels. Published by A.M. I. Second Printing, 1983
20-2 or b as you will. ERF 686 Truck, dark blue body, silver radiator, headlights and bumper. No.20 cast on black base. 8 plastic wheels on 4 axles, "Ever Ready for LIfe" decal on sides of body. 2 5/8", 1959
7 variations Wheels and axles described as:
a) small dark gray plastic, crimped
b) small dark gray plastic, rounded
c) small light gray plastic, rounded
d) large dark gray plastic, rounded
e) large light gray plastic, rounded
f) small silver plastic, rounded
g) small black plastic, rounded
There won't be may silver wheeled models out there. This book also has a number system to tell value. You would need 15 comperable models to trade for one of these silver wheeled versions where al the rest would need 8 and the last variation would need 7. That is how I read the system in the front of the book. I can clarify further if anyone wants.