Keep an eye on your local Craigslist or facebook marketplace for a 2wd Ram with a V10 automatic in it. You can get the whole truck for about a quarter of the price of the re-builds you listed.

Dump the 413 and put the V10 auto in your RV. You will be miles ahead.

If you still want to keep the 413, go to the autowrecker and they will do a search for you for a pre-1998 47rh. You will probably get one for under a thousand dollars and get a 30 day warranty.