look for a 59 3 on the tree car, 6 cylinder will likely work (they just have a bracket that holds the ball on the block side of the Zbar), lots of them sold new so should be some around, get everything Paul lists from the over center spring under the dash, pedals, rod through the firewall, zbar bracket on frame, zbar, lower rods, lower springs, and clutch fork if there. I wouldn't be surprised if the setup from a 60 was the same, but I have no experience with a 60, I assume the hole in the firewall for the clutch to zbar rod is the same 59, 60. If that hole is the same, but something else is different, like say clutch pedal, take everything from the 60 and it should work together, it is just geometry.
I like the cast iron bell housings with the starter mount, you never have to worry about starter alignment, but you have to use a 168 tooth flywheel. If you are using a 168 tooth and want an aluminum BH, you need the BH with a bump on the bottom. Not sure what does or does not work with a BB, bell housing wise.
The rubber seal on the firewall and the plastic rubber inside- the automatic ones might have a round spot that you can remove for the clutch rod to go through.
The 59 had no metal plate on the hump for mounting the shifter, I'd recommend you use the one for a 60, it really helps line things up for the shifter boot.
I had a 283 PG and switched to a 4 speed. They ran exactly the same setup with the 409 in the 59, no issues at all. I got a complete setup from a guy who was switching his 59 from a 4 speed to a T350, I got lucky.
Good luck with your conversion, well worth it. I'm still not old enough to drive an automatic.
Don