This honing jig uses a decorator's seaming roller which lets you use the whole length of the stone and doesn't crush its surface.
Since you have had to remove the lever cap to remove the iron, it can be used to clamp the iron to the jig.
Form a tenon on the end of the wooden handle that came with the roller.
The projection of the blade beyond the end of the jig fixes the angle (30deg).
The easiest way to find this is to use either and 'angle finder' spirit level or an electronic 'Bevel Block'.
To repeat the angle, I just rest the end of the jig against the edge of the bench and align the edge with a mark on the bench top
The length of the roller arm from the upper surface of the holder to the outer circumference of the roller is 160mm (approx 6 -1/4").
The holder is 220mm (approx 8-3/4") long. It is the same width as the iron.
The screw fits into a pronged 'tee nut' on the underside of the holder. Any suitable nut will do, especially if you epoxy it into place.
These dimensions are based on an oilstone whose top surface is 41mm (1-5/8") above the bench top.
A piece of aluminium angle screwed to the underside of the holder serves as a guide to the iron, but it is not essential.
I made this after 40-odd years of freehand honing and am now a convert. It will not hold chisels however!
To obtain a working drawing, transfer the image to a Photo Editor using 'Save Picture As'. Print, adjusting the settings until the width of the holder prints out at 2" (50.8mm).