I've also had this problem when fitting reaction bars, and like Button says, sometimes sleeping on it works best.
The kingpin can shift slightly as the bolt comes out, and alignment is crucial to get it back in.
I loosen the chassis end of the Brake Reaction Bar so it floats free of the KP bolt.
Because I make My own King Pins out of 1" Hydraulic Rod I tap both ends 1/2 NF SAE (if I lived in the UK I would probably used Metric).
Instead of the Original KP Bolt I purchase 1/2-20X1.3/4" Set Screw Socket Cup. (The neat things about these set screws is then can be turned with a allen wrench) Top and bottom bolts. I use new stainless nylock nuts each time I remove them and blue loctite on the threads of the setscrews..
Now when I insert the KP I have the bottom plate attached and I screw the setscrew into the top with the allen head cup at the top.
I use threaded rod to move the KP into position using the bottom plates. (Threaded rod about 6" long with two nuts jammed at one end for easy turning - I often use an air wrench for quick work)
Ordinarily the top setscrew finds it way into the top hole. If not I can use a allen wrench to get it into place..
Mind You I live 1,000 miles from the nearest Morgan Dealer. I must be self sufficient. Not hard, just takes a little imagination. Also tools or Morgan Friends nearby who have the tools and expertise.
