yeah a manual with a fat sector would normally be 24:1 i think....
aint nobody gonna make a specific 16:1 ballnut and screw for a fat sector box in my opinion
tooling it and cost/minium order would be hard enough without having to do it twice.
16:1 is really for A bodies only, the bigger cars really need 20:1 or 24:1
So i'll take it until i know different that both fat and thin sector boxes use the same ballnut and screw part... i.e a guess based on whats be said.
You could get a Lares Rebuilt/new in 16:1 20:1 or 24:1 and a new pitman arm for the small sector box and fit that.
Or here is my rebuild and conversion to RHD for a small sector australian box
yu could apply what you see to your box, with slight alterations to part selection.
Manual steering box rebuild - Mopar Muscle Association UK
believe the ballnut and screw and asscoaited seal are still the same for your big sector box
but you will need a lower sector seal from a big sector box . or potentially the lower sector seal off a big sector power box would do....
when it comes to big sector drawn cup roller bearings you will have to work with part numbers on what is in there.... so avoid bashing the number up when you push out the bearings with a socket on an extension.
get a long one for the bottom bearing... it will have a short one at the moment.
if you can't get top cover bearing out just remove needles and reload with the new ones. the top bearing has the least hard job
Dave