Hi George,
Your museum is one of my very favorites in the NY area. I always recommend a visit there to folks visiting from out of town.
I am not entirely sure what you mean by rigging specifications.
In general I would just emphasize the importance of utilizing the services of a reputable Fine Arts Service company. Even highly regarded professional riggers should be overseen by someone who specializes in handling/moving art - there are more aspects than just the lifting part that are critical you your project.
Ultimately as the caretaker of your collection you are ultimately responsible for the outcome so be sure to discuss your concerns and make sure that you are confident that whoever has been hire has addressed them thoughly before the work starts. As well be sure to communicate specific information that may not be apparent by casual observation to an outside viewer.
A good example would be a project that I worked on while employed by a major FAS company many moons ago. It was at your museum and it involved a large stone sculpture to be crated and sent to DC. We were told two things that we wouldn't have know unless forwarned. One was that the surface of the stone was polished flat and smooth in some areas and had been left with its original surface in others. We were told that it had recently been conserved and in fact the natural surface had very active spalling. After conservation - just looking at it - we would never have known how important it was to avoid it. The second detail was that before being crated it had to be lifted off of a large metal pin that was actually holding it upright. Visually it appeared that it could be set down on the smallish flat surface area around the pin. In fact without the support of pin the whole piece would have fallen right over - what an unfortunate surprise that would have been!
By having the warning though we were able to make arrangements for the piece to be lifted with the rigging left in place for a couple of days to build the very substantial crate that it required, around it while suspended.
A lot of rigging can done in house of course if you have experienced staff. There are folks who provide training - Methods and Materials is one. The more you know the better off you are of course.
I may have failed to understand the question. If so please feel free to re phrase it and I might do better.
Cheers,

Ashley