Jumping gears.

[BA80]

It takes VERY LITTLE rounding on those dogs to cause a slip. Not very likely the forks are bent.

[crazy steve]

Those look good... You've got signs of normal wear on first gear, but that seems to be typical. Second gear looks excellent, I wouldn't hesitate to put the pan back on and run these as they are...

As to the difference between 'just tear it down' and 'run before restore', as James point out it's not always practical. You can end up duplicating a lot of work getting it running; there can be a big cosmetic difference between a repaired assembly needed to run it and a restored one. Or the cost of acquiring missing parts in some cases.

Granted, running the bike before teardown can illustrate issues rather quickly. But I've found that pretty much anything can be checked on a non-running bike well enough to determine just how bad it is. A thorough visual inspection will take care of a lot, and if I'm doing a painstaking, thorough restoration or rebuild I've already figured that I'll be going through the fuel/electrical systems bit by bit, finding any problems along the way.

The one major unknown is always the motor/trans; how good is it? This can be a judgment call to a degree, as there are a few items that may not lend themselves to diagnosis on a motor out of the bike; oiling system problems and excessive bearing wear to name two. But most of these type issues are extremely rare on these bikes as long as there's not a ton of miles on them. That leaves the condition of the trans, rings, and valves as the main items to check. James just did the trans inspection, going through the process of a valve adjustment then compression test will give you the mechanical health of the top end. What you find when you pull the various covers can tell you a lot also. I've also found this is a lot easier to do with the motor out...

If the motor checks good on those three main items, I feel confident in reinstalling it; most anything I find after getting it running can be addressed without pulling the motor. And if it does check bad, then I can decide on whether or not to get a replacement. The replacement probably won't have a bike attached, so the same checks would apply. If you decide not to fix the bike, it's already broke down into spares....