Basically, David is right on the money. If ball joints are bad, replace them and work your way out (spindles, disc brakes, etc). It is true that the Haynes manual you speak of shows about 6 or so bolts that stand in the way of you having your new axle beam. What it doesn't mention is that if your frame head is fortified with rust, you could be in a world of hurt if things start breaking off (or stripping out) in there-I've run into this a couple of times in the recent past on customer cars. Another note: beware of inexpensive front disc brake kits out there for '67 and down bugs. What they only mention in that really fine print is the cheap kits will leave you with 4-lug front wheels. If you're not into mis-matched wheels or adapters, the price for true 5-lug conversions is SIGNIFICANTLY higher.
P.S. if you intend on using adapters, be aware that they will throw your wheels futher outward as will most available dropped spindles if you're thinking about those too. 1/2" to 5/8" doesn't seem like a lot untill your tires drag the lip of your fender...not a good deal when you've just forked over all that money for a new front end.