1938 Fargo FG3-59

As suggested there is bound to be rust around that tube unless you can get a little camera down and around it via a welsh that has been removed. They would not be hard to reproduce especially if you have the old one to go by.
If it is a case of getting it running first to see what happens that is fine as you should be able to pull the water pump and radiator out and gain access to start collapsing the old one down and pull it out.

If you have any Chrysler manual of the period they tell you how to remove the tube. As mentioned above badly corroded tubes may require breaking up and hooking out with a length of rod and running water to flush the broken bits away.

There are thousands of Chrysler flat 6 engines driving perfectly well with missing or badly corroded tubes but the factory must have thought they were essential to go to so much design trouble.

Vintage Power Wagons and many others have lifetime stainless replacements for about $50. They even have a specially designed puller!

Download the Vintage Power Wagon catalog on line for thousands of period parts.

When I was doing the David Bron engine up I thought about this distributuion tube a lot. From the feed back I got it was there to dirct water to the valve guide area in the head to keep them cool. Many said they would not put one back in the head of a tractor in our climate and ohers said to fit a new one.
The more I thought about it the more I wanted to fit one so that the guides were kept cool. So I sourced one locally in Newcastle and made of stainless steel. So after the ehad was reconditioned I then fitted the new tube. I had to be very careful as to which way it went in. As you had to align the holes in the tube with the valve guides so I sat it on top of the head next to the valves. Yes, it will go in the wrong way if your not careful so after aligning everything I fitted it in annd then dressed the ends over to keep it in place.

The Chrysler one is just a loose fit and can usually be moved with only your fingers. It is trimmed flat to the face and the water pump just holds it in position. Once corroded can be a fiddly, if not technical, job to get it out. It is a sort of triangular shape so will only go in one way easily.

Maybe a tin rod that can fit up the opening with a small hook on the end to find a hole then work it back and forth. I would also try a length of #8 fencing wire obtainable at your nearest farm fence and keep working that back n forth and get as much loose rust out. I know I have not regretted doing mine as it is one less thing to have to go back and visit with a boiling radiator on the side of the road.

Cobba,
Now you know as well as I, that any self respecting drover/ wheel attendant would have besides the mandatory roll of toilet paper, bottle of port ( Stones green ginger wine in winter), phillips head screwdriver , a pair of side cutting fencing pliers in his too bag/box!

Who knows when you have to jump the cockies fence and help yourself to a cupla feet of 8 gauge?
Spin a dual tyre spacer? Make an extra spacer outta wire!
Blocked radiator?
8 gauge fencing wire rods the tubes out!
Bolts fall out of plastic mudguard bracket and start scrubbing out on tyres?
Wire 'em back up with the ubiquitous universal 8 gauge fencing wire?

AND, cockies know and understand that when they get a phone call from the local poundkeeper, that another battling truckie has had to do an emergency midnight fix!
Dave_64