If you look at the back of the chuck (remove any backplate) you should see 4 large circular discs, these are infact the end of the “bearings” which look like this. They may be tapped for a puller. Once remmoced there is nothing to retain the screws

Bit of 4-jaw servicing going on here which shows them being removed

Remove the jaws and gently tap the end of the fork from the front face with something like a thin screwdriver or anything that will fit between the screw and the chuck body. Generally they are a light press fit. In use tightening the chuck jaw screws keeps them firmly in place. Some but not all chucks have small cheese head screws half in the body half in the fork, these would obviously need to be removed first.

I bought a NOS 6″ four jaw independent Toolmex made in Poland which had an integral Myford thread and wanted to convert it to front mount on a backplate for the Smart & Brown model A which is 1 3/4″X 8W thread. I decided to remove all of the screws and started by numbering the plugs and rear of the body as they had little screws in the joints. I had to make a special punch tool to push the plugs out, maybe more than one, I can’t remember. On assembly it was tricky to get the plugs exactly aligned so the locking screws could still be fitted. Chucks do not always have the screws, Pratts do not but both versions are very tight in the body.

Are you sure you cannot fix the tightness without taking the thing to bits? You might get away with slightly moving the plug and be able to remove whetever is stuck in the works.

Those forked retainers are usually heat treated steel as the forces on the fork are quite high. Silver steel would be a suitable material and after finishing the shape you could heat it red hot and quench it for glass hardness. Then clean up the fork so that the silver of the metal is showing and heat slowly until the fork goes from light straw to dark straw and then starts going blue. Then quench and it should be strong enough. If my heat treatment advice is faulty, there wil be more informed replies.

By all means try to reclaim the old one if there is enough material in it but you will probably need solid carbide endmills for the job.