Ok,
So here are the options for a SOHC 69-76 K or F bike:
1) Convert your existing setup. The hard part here is figuring out the speedo drive. The old way was to get K0 parts but since they are hard to come by these days you will have to modify your existing setup or test fit cb550 parts till they fit (I know there is at least one year that works but I don't know what year - perhaps 74?).
some links:
http://www.sohc4.us/forums/index.php?topic=2582.msg171561#msg171561
www.sohc4.us
2) Get a 1975-1977 GL1000 Goldwing front end. You will need everything from the triple trees to the brakes. This is a bolt on but you are on your own as to how to mount the gauges.
AS for DOHC parts on SOHC bikes. You can use the DOHC F swingarm, but you will need to cut down the pivot point to fit (not hard, just take careful measurements). The front end I do not think is a bolt on but the later 77-78 SOHC F's used a similar front end that is a bolt on (provided you get the trees). I am not sure about the chain line, but I think if you use a 1979 wheel it may not be a problem.
All the F bikes are rear disc. YOu can get a comstar with drum for the rear but it will have to come from a K or C and it will likely be 16".
The easiest way I can think of for putting a rear Disc on an early K bike is to get a 1975-76 F rear end (the whole thing, swingarm to rim). It will be a spoked rim and it will bolt into your frame. The only mod you will have to do is make a mount for the master cylinder for the rear brake.
Personally, if I were you I would look for a 1975-77 GL1000 (with spoked rims the comstar won't work) do get you dual disc up front and keep your drum in the rear. Honda discs from this era were succeptible to decreased braking in the rain and the drum doesn't have those problems. If you must have a rear disc then look for the 75-76 F to snatch a setup from.
IF you really really want comstars I would look for a 1977-78 F rolling chassis in your area and just strip the front and rear to work on your bike. Be warned the 1977-78 front end pieces are not interchangible with the earlier pieces you will need the trees to convert. The same goes in the rear. The general rule is that if it has comstars then it won't work with spokes. Once you have the comstars if you want better brakes you can upgrade to the 1982 2 piston calipers on the cb750F and 900F
