Combining two RT instances

Our organization recently took over a project from another, and we both
use RT. Now, we have two RT instances running here. I’d like to combine
them so that all of the old tickets from both instances appear in one RT

I have considered selecting from one database into the other, but am
concerened about overlapping ticket numbers. I could probably get around
that, but I am certain that there will be many things I’ll overlook,
such as ticket relationships. I’m not concerned about users, groups,
templates, or scrips. Getting the tickets from one to the other would be
great. I could even deal with having them all in the same queue.

Is there anyone who has successfully done this and has any advice one
this? I didn’t see anything similar to this in the list archives, in the
wiki or a general google search, but I may have overlooked something.

I’ll take any advice you can offer.