The 20-tooth driven gear for a 3.36 axle is in the "small" family (0.8" O.D.), and is blue nylon; it's used with the "large" 8-tooth DRIVE gear (1.85" O.D., .610" thick) and mates with the 18-22-tooth nylon gears that cover 3.08 to 3.70 axles.
The 20-tooth STEEL driven gear is in the "large"(0.87" O.D.) family, and was only used with a special "small" (1.77" O.D.) 6-tooth DRIVE gear; this combination was ONLY used with the 4.56 axle.
Visually, both of the standard 8-tooth DRIVE gears show six full teeth across the gear face, and the special 6-tooth for the 4.56 axle shows four full teeth across the gear face.
With a 3.36 axle, I'd build it as a wide-ratio.