I've done several 6-to-7 upgrades.
Some were just a matter of switching the freewheels.
Some required a couple of spacers.
Some needed re-spacing and re-dishing.
It's going to depend on your hubs and how close the small cog it to the drive side drop-out.
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You know it's going to be a good day when the stem and seatpost come right out.
(looking for a picture and not seeing it? Thank the Photobucket fiasco.PM me and I'll link it up.)