Option for budget manual transmission upgrade

[Accelo]

Around these parts, a SM465 is the only thing left over when the rest of the truck is junked.
I went to the Portland Swap Meet once you and I could have filled the back of a dump truck with them.
The cheapest option is to replace it with used. $75 buck should do.
However, if the truck is driven a lot, an overdrive would be a great addition.
Have you considered retrofitting an automatic?
The manual may keep his buddies from driving it if it!