John,
Craning a locomotive is not always a bad thing. True, if it can be avoided it should, but if you have no other choice it can be done without hurting it. I was recently involved with moving an operable standard gauge 2-8-0 (Great Western 51) from California to Colorado and we had no choice but to crane it at both ends. Anyway we did it in roughly the same manner as you are proposing and #51 lived through it with no ill effects. #315 is light enough (relativley speaking) that it should do just fine. The key is to have someone who is familiar with steam locomotives on hand to guide the crane riggers as to what they can and can not do to the locomotive.
A loading ramp is always preferable, but when you have no choice a crane is capable of doing the job just fine without hurting the locomotive. (As a result of its use in movies over the years, Great Western 51 has been craned many times, always without ill effects, just go slow and be careful and keep an eye on everything)
Jason Midyette