A 1-1/2 steerer tube has an outer diameter of 38.1 expanding to 40mm where the crown race sits, much like a traditional 1-1/8 steerer is 28.6mm expanding to 30mm for the crown race.
A standard straight headtube for 1-1/2 forks has 49mm ID see the one on the extreme right of the image below (labelled "1.5""). Much like the straight headtube for 1-1/8 forks which has 34mm ID (extreme left labelled "traditional").
Lots of modern headtubes made for tapered headsets have a 44 upper ID and either a 56mm lower (labelled above as "Tapered/E2") or 44mm lower (labelled above as "Integral"). Even the old Giant from 2005 (first model Trance) sitting in my shed is 44mm upper and lower.
Both of those headtubes (Tapered and Integral) can take a lower cup that accommodates a 1.5" (i.e. the lower part of a tapered steerer tube). Hope don't make an upper cup that can accommodate a 1-1/2 steerer for a headtube with a 44mm ID, but the upper headset cups in the link from earlier is a Reset racing model made for that configuration.
Here is the line up chart from Reset racing. #7807 upper (Oberteile) and #7089 lower (Unterteile) would convert an Integral head set and the lower would need to change to #7086 for a tapered. Note the upper has a 16mm stack height (Aufbauhohe) above the headtube.
