Thank you all for your replies. I certainly wished I had measured the spring before I left the trailer, but the circumstances didn't allow it. I do plan to replace both springs at the same time...thanks for confirming that's the right thing to do. It would be a 5 hour round trip, so I'm going to try a little harder to get measurements before I take a trip out just to measure. :)
A couple of additional questions:
I've heard people mention replacing with springs rated for a higher weight...wouldn't this mean a stiffer spring, and hence a stiffer ride? It gets the **** rattled out of it anyway, and I'd be concerned about the additional wear that would cause.
Time2roll mentioned upgrading to a wet bolt kit. What is that? I'm all for making improvements.
I have not attempted this type of repair before, but I have no doubt I am capable. I can imagine supporting the frame in front of and behind the axle with jack stands, and then supporting the axle itself with a jack to remove the spring. Any other pointers?
Thanks again,
Jason