While I agree that the disc brakes should be used on the front that also assumes bikehorn has a disc brake mount on the front hub.
It isn't a small fortune to get the caliper, rotor and a 26 inch disc brake wheel (especially used on ebay and from local sellers) it is more than the free of using scrap to make a drop bolt.
Braking, followed by dialing in the fit of your bike are the most valuable upgrades in terms of how much better it makes the riding experience and cost effectiveness. It is always amazing how much better discs stop in the wet compared to rim brakes.
These tips apply to any kind of bike with any kind of handlebar. Getting things dialed in so you aren't stretched out or cramped up makes a world of difference.