The biggest prob w/disk brake conversions is the wheelset - the hub(s) aren't set up for disk(s), combine this with a lack of mounting tabs and it starts to get real costly. I'm considering buying a Walmart bike just for the front shocks (mount tabs), wheelset, and disks. I'd still replace the calipers as I've heard horrid things about them, primarily that you cant adjust the pads and they squeal like ****. If ya wanna do that, just be sure to check head tube size and hub width.
Yet azbill's suggestion of a front drum would be the way to go for your bike, needing only to replace the spokes and re-lace the front rim (mebbe zot a tab on the forks) I think it would look
sweet on yer ride and I've heard great things about their stopping power and wear rate

You could check springer forks, many are inexpensive and have the needed tab. (and those would look real nice on yer bike too)
Very sharp looking bike BTW, I like the classy black & white theme! The small signs of wear only means you love it and use it all the time. My bike for one is usually
covered in mud lol