You're going to have to pull the bearing carrier all the way out for two reasons.
1. You will need to access the shift cam so that you can actually install the shift shaft back into it.
2. Once you start removing the bearing carrier, even if it's just an inch, you're more than likely going to ruin the seals.
The real question is, will you have to remove the driveshaft after you pull the bearing carrier out (in order to pull out the forward gear, so that you can access the shift cam behind it.) You might be able to get lucky, and re-insert the shift shaft back into the cam while the forward gear is still in place. But if it's fallen out of place, you have to take out the driveshaft in order to pull the forward gear out. It's not very hard, but some special tools are needed. Luckily you don't have to worry about pounding out bearing races and re-shimming them, etc. I would definitely order a complete seal kit for the lower unit as well.
I am also not sure how mechanically comfortable you are with this kind of work, so if what I said intimidates you, you might want to have a professional do this.
