Gary Fairbanks is one of the best 915 men around. Great service - he will send you a purpose built crate to ship your tranny, and return it finished in a similar crate. Prices are very reasonable.
If you can sweet talk Marc into doing it, you will get a superb rebuild and have a chance to see it all done, which is the best way to learn. With luck, Marc will give you a break on his daytime hourly rate
Be careful with Vertex. Some guys have great stories, but there are others as well. They are almost always the cheapest price, but the quality control is not what it could be from what you see posted around the boards. I have no personal experience with their rebuilt stuff.