I wonder if it's really not self-explanatory...
tapering:
You just buy some OS tubing(I.D. 1-1/4", O.D- 1-3/8"), the min length is ~90-100 mm (depends on the height of a hic shim), you need about 30mm(1"-1.5") of overlapping: for instance, your bar is now 53 cm high and you want it to be 57, you...