Originally Posted by
shelbyfv
You aren't likely to find a light frame that will take 42s. For that you'll be looking at touring or gravel frames. You may be able to convert a road frame to 650b, that will require careful planning and measurement and 38s may be the limit.
And in that case you essentially asking "can a steel 650b bike be built that is 20 # or less, not can a steel bike be built which is less than 20#.