Indexed headset - repair or replace?

I have a Bob Jackson Vigorelli. It's a steel frame of course.

Here is the conversation I have had with them

Me

Is there any technical reason I shouldn't have the threadless forks cut down and treaded to enable a quill stem to be installed?

Them

You will not be able to do this as the columns are too hard and will not cut very well. The only way to go from a 1" Threadless to 1" threaded is to change the column.

The whole process may cost almost £75 by the time I add in postage.

A bit pricey just to downgrade my fork to an old technology.