Originally Posted by Treefox
I did precisely this conversion this past autumn. Took an RX100 7-speed drivetrain, swapped out the rear wheel (hub totally crapped out on mile 3 of an 87 mile ride... but I still finished - quite the workout), so I got new set of Shimano RH550 wheels, chain, cassette, Tiagra STI levers, and because it was cheap, a new 105 RD. Kept the FD and cranks (no problem with the spacing at all).
I had no trouble squeezing the new wheel into the narrower dropouts. It's a bit snug, but not terribly to squeeze in by hand - even when fixing flats on the side of the road. Though it's a steel frame.
I don't understand how the hub could "totally crap out" and yet you finished the ride. Could you expand on that?
Next time you have the bike in your local shop you might want to ask them to re-space the rear triangle. It's cheap, fast and easy and it ends up making putting in the rear wheel a lot nicer.
I've done the sort of conversion that you've done a couple of times and I agree that it is the best way to go.
When you hamfist something it usually comes back to bite you on the butt at the worst possible time.