Hi Ray,
The spacer ring lifts the Monza cap .250 so the Locking Cap will fit under the Monza cap. The neck of the filler tube protrudes too high for the Monza cap to latch with the Locking cap underneath. So your choices are 1) shorten the filler neck by .250 or 2) raise the Monza cap.
The safest way to grind down the filler necks is with the fuel cells removed from the car. Since this requires taking off the hood and front suspension, spacing up the Monza cap .250 starts to sound pretty appealing
The difference is barely visable although in both cases, with or without the spacer you have the opportunity to make sure the cowl is sealed to the base of the Monza cap. Some cars were not adequately seated in fuel proof sealer which results in an amazing amount of fuel smells in the cabin if the filler backs up on you...
So it's a practical enhancement to the car, good way to kill a few hours of spare time and makes the car cleaner and safer. Two sets gone today, can I put you down for a pair while they're in stock?
Thanks for the pics of your car btw, looks great!
Cheers