Vintage Brake has posted a nice summary of some of the more popular brakes out there. I've heard nothing but good things about the work this guy does so if you're in the market it's a good site to check out. He doesn't seem to be very fond of the Grieca 180 in his comments, but in an e-mail to me he had a more positive view of the recent hubs he'd seen.
My first thought for this bike was to use a CB350 brake plate mounted in the stock Ducati hub. I went so far as to buy a CB350 wheel, then realized the CB350 brake is narrower than a Ducati brake. It would have worked, but I decided I wanted something better. Well... at least prettier. Next step was another Honda brake off a CB77. I found one on eBay but it looked a little beat up so I continued looking, including looking for other options.
I had just about settled on a new Grimeca 180mm brake similar to the one used on the later Ducati singles when I stumbled onto an Oldani replica at Disco Volante Moto. I made an offer on it and after a few more e-mails it showed up on my doorstep early the next week. It's also a 180mm hub and according to numbers I've seen, weighs a pound or two less than the Grimeca. Note that the picture above shows two front brakes - I only bought one, the picture is stolen off Disco Volante Moto's website.
When it's all said and done, the only original parts left on this bike may well be the frame, swingarm, and rear brake. There are fancier brakes out there for sure, but I have to draw the line somewhere. If I decide I just have to have something fancy back there, I've seen an aftermarket brake plate complete with cooling duct. Problem is it costs more than what I paid for the whole bike to begin with!