I have an early 80's 12speed Fuji sports tourer that I use for touring and I have recently replaced the gearing on it cheaply.It has touring geometry but without all the brazeons and originally geared similar to a road bike.It does have an attachment point on the rear dropout for a rack which I then clamped to the rear seat stays with no problem.But I understand even w/o that you can use an Old Man Mtn rack if you can find one cheaply perhaps on ebay.

I assume being a long distance backpacker you have light(ultralight)weight gear which would make touring long distance with just rear rack feasable and would also be essential if your bike isn't ideally suited geometrically for touring with heavy loads.

As to the gearing for the rear check out the new shimano hyperglide multirange cassette/freewheels.I got a 6speed 12-34 freewheel online for around $10-12 not including shipping from great american. I believe others such as bikeman and AEbikes also had similar prices but in some cases wouldn't ship online per agreement with shimano.I believe with theultralow rear gearing you will need a mtn bike derailler but luckily i had replaced my rear derailler about a year earlier with a $20(incl. labor)cheap mtn derailler at the lbs. For chainrings I stayed with double chainrings to remain with 12 overall speeds and went with 34/44 tooth stronglights I found real cheap on closeout on the thorusa site(I believe $14-15 for both plus $5shipping).This gives a low ratio suitable for touring around Fl but for cc you may want to go the triple route to get lower gearing .You don't really need alot of gears just the right gears ie a few low for climbing a few mid range for everyday cruising and maybe a high or two for decents.

As far as hubs,cranks,bbs and the like i didn't really bother with all that preferring to keep things simple but between the advice you get here and various online sites I am sure it is well w/in the feasability of a motivated do-it-yourselfer.

I suggest to avoid confusion you first determine the gearing you want/need then figure all the nuances of spacing compatiblity etc. to minimize undue confusion . Good Luck