Yep, it's an older bag. In fact, the reason for my asking right now is that it's about time to replace (or refurbish) this bag, so if I botch it entirely it's no big deal. Plus I do have quite a lot of project sewing experience so I'm not too worried about the construction part of it all.

If I do get up the gumption to take this project on I'll post the results in DIY.

One thing I like about the half-bag idea is that it'll lead to a bit more gear reuse by pressing my down jacket into sleeping bag service, with a net reduction in gear of about a half of a sleeping bag. Sounds win-win to me.