I haven't done an 803 in a while, but the last one I did I used a piece of 1/4" thick rigid plastic for the spacer ring.
I made it just slightly bigger than the diameter of the float and rather than a circle it was more of an oblong triangle ( helps get it through the opening of the tank easier.
Drilled a hole in the center that was a tight fit around the knob on the bottom of the sender and epoxied the spacer to the SS sender with JB Quick weld ( yellow and black tubes )
Be sure to orient the "Triangle" so that one of the points is facing 6:00 when looking at the top of the sender with the wires at 3:00.
Make your plastic a triangle, an oval, whatever.... it's diameter needs to be about the same size or even slightly bigger than the hole in the tank, so make it easy on yourself to install it!