disk brakes not cool

Best braking...or good braking?
Best will cost you a bundle...say $1200-1500 by the time you get it laced up. (big Grimeca, Fontana etc)
Very good will cost you $500-600 laced up. (Suz GT750 220mm)
Good will cost you around $300-400 laced up. (Honda 305/450, Suzuki T500, Yamaha 650, Kawi h1 (early) 200mm).

This includes a spoke kit and probably a new alloy rim. Spoke kits go for about $80, decent alloy rim (Japanese or Euro, not Chinese) $150. Most of the time you can't use the orginal rim because the spoke holes in the rim are angled different since they are aimed at the small OD disk brake hub....when you throw on an 8" diameter drum hub the spoke angle is way different.

Might be cheaper to go with the entire front wheel of one of these bikes...assuming it's the same diameter, uses the same axle size, is not too wide. But then you'll have to deal with things like a different speedo drive, different brake stay arrangement etc.

To do it right it's a considerable undertaking. And you'll probably end up with a brake that doesn't work as well as a well setup single disk.
JohnnyB

Good choices.
You can lace that hub to the XS alloy wheel no problem. The T500 is a 15mm axle...so you'll need to take that into consideration...I'm not sure what the axle size is on the Honda but I'm guessing it's 15mm also. The T500 hub uses a "lug" style stay on the hub....the honda forks are disks so they won't have a lug or a stay bolt....typically you can make your own stay and bolt to a caliper bolt hole in the fork...a little more difficult on the drum side....I've drilled and tapped the bosses on either side of a T500 lug and used those to mount the stay to the drum. Or you can fabricate a piece that bolts to the Honda fork and engages the lug on the T500.

The T500 drum may have to be narrowed up a bit to fit between the Honda forks...and of course the speedo drive is going to be all different. It can be done...and has been done by plenty of people racing the Hondas....but they don't have to worry about a speedo. A lot depends on your access to tools...if you, or a friend can use a lath and milling machine you can make any parts you need to make it work.

It's not a bolt on proposition...but neither is it that difficult. I run a T500 drum on my race bike with Honda 550/4 disk forks.
JohnnyB

Eric,
Yep I do all the work on the brakes....typical stuff is shown here:

http://www.jrbranson.com/showandtell.htm

I also sell 305/450 Honda hubs all ready to go, around $225 including new shoes, bearings, vented, lightly polished. The same for T500 around $325 (prefer to save these for race customers as they are getting harder to come by).

These are not "bolt on", they are generally intended for racers that know the in's and out's of how do adapt a drum to their bike. So they don't come with a lot of customer support

I've sold a few to the guys here that race. That said....in general on a street bike I agree with Geeto...I'll take the power of the disk brake. I'm assuming you have a CB350G (1973) with the smallish single disk up front. I love disk brakes....only reason I do the drums is cause I need them in my race class...and I have the machines to do the work.
JohnnyB