Hi Dan,
I think that 9E would be too early for your car, but it might be wise to pick it up if it's not too expensive as it might take a while to hunt down the correct box. It's funny, but the Auto transmissions should be around, but nobody saved them when the scrapped the cars so they can be a lot harder than the corresponding 4 speeds. A good example is the 69 CJ cars, I know of about a dozen RUG AE2 boxes for sale currently, I've come across 1 or 2 Mustang CJ transmissions for sale in the last year or so. The CJ Autos are worth about twice what a 428 4 speed transmission is worth .....
I wouldn't bother changing the valve body as the difference is probably very minor. As Jeff mentioned, nobody reproduced the Transmission tags currently so that's a problem .....
Hope this helps, John