As a general rule the most expensive road bike component is the 'brifters'. Brifters also have short brake cable pull and most flat bar bikes are equipped with long pull linear pull brakes. A topic that I don't know enough about is top tube length. When you replace the handlebars, how is that going to be affected?

It can be done but it's going to be pricy and there is a good chance that you won't be completely satisfied with the result.