The Roadranger transmissions are not synchronized. Only the air operated range shift is synchronized.
The manual advises you to use the clutch for every shift, although most often people shift them without using the clutch.
Yes, the 4-53T weighs approximately 1,200 lb, and yes they can make some noise but with a muffler can be reasonably quiet. Not sure about "a little hard to control emissions" if tuned properly they are as clean or cleaner than other engines of the same age.
A 6BT is longer than a 4-53, and while a great engine probably takes a fair amount more work to install in an AD truck. I've seen pictures of a few 6BT's in AD trucks, but haven't seen a clean and professional looking one yet. So not having tried a 6BT myself that leads me to believe it's not so easy.
Grigg
