For the record... the arms are original to my 1980 Mini that I bought in '94.  I doubt that they were ever modified...

Either way, thanks all for the advice.  For now they are going into the ol molasses bath for a while, then we'll see what they look like.

I have all winter to figure it out!!

Sorry. Wasn't trying to imply that the part was never factory. The one he posted just seems to be an uprated aftermarket piece on all the sites I could find. They call it a "competition" piece on every site I could find.

I was just stating that my car (an 80's car) didn't have that from the factory, so his may have been similar. I think we're saying the same thing in different ways. haha.

Wither way, I think we all agree that you should replace it with one of the options posted. haha. Let us know when you get it out.

Yes it was definitely not an aftermarket part.

More clarity needed, I guess. Up until the early 70s, all dry suspension Minis used 2A4337 which looks like C-AJJ3361; i.e, one part threaded on both ends and a fixed spacer. (See CooperTune's post.) Repairs were often made to save money by using a long bolt and the 21A2694 spacer.That set up became regular maybe 73 or 74. Never bothered to figure it out.

You're likely going to have to replace the bolt. I would regardless of how well it eventually comes out. The spacer you may be able to save following suggestions given in other answers. If not: 21A2694.

My arms were original with original hardware, and the bolt on both sides was a 3/8" UNF x 4-1/2". It was nothing more than a high tensile bolt. The spacer on my car wasn't an after thought or a fix due to someone fitting a standard bolt. It was a factory piece as well. Looked identical to the OP's arm and almost every late model mini's suspension I've ever worked on. I replaced it with a bolt with a proven high sheer strength and cleaned everything up.

The aftermarket piece you've posted with threads on both sides looks nice, but it's certainly not what came on my car from the factory. Not sure I'd pay the host $36 for them with the availability of a very high quality bolt around $2 ea.

To each his own. For the OP, You'll be more than fine killing the bolt that's in there now and replacing with the bolt dimensions I stated above. Or buy the part Cheleker posted. Choice is yours.

Correcting my post on the 20th. Didn't pay attention to the photos provided. Responded based on the many times I've had to pull off the shock metal piece!

The arm as it originally looked is part number 2A4337 and is not a simple bolt. See C-AJJ3361 if the 2A one doesn't show any more. Note threaded ends on both ends, and the spacer as part of the bolt, not a separate part. Then see 21A2694. As indicated, the original 2A was often replaced with a regular bolt therefore needed the big spacer.

Your arms are the same as mine. That "pin" is literally just a long bolt. I wouldn't pay any crazy price for the "pin", but I would instead do like I did and go out to find the highest quality bolt of matching dimensions you can. In my case. I went straight to Fastenal and got the exact specs of the bolt and bought a very strong, high quality replacement for both sides.

As for removal, you can do it many ways, but don't damage the spacer or the arm. I had to heat the bolt and also used a high quality penetrator fluid. I was then able to get the spacer to separate with a big ass set of vise grips on the spacer and a wrench on the head of the bolt. Then once the spacer was off, I could drive the pin out with my 5lb sledge hammer and the arm in a bench vise.

TL;DR - Heat, Penetrating fluid, and a big damn hammer

The problem being there are two front upper arm shock pins. Early was a pin with a built in spacer held in place with a nut and loc washer to upper arm. Later I don't know when it became a long bolt with a slip on spacer. I have a pile of the arms I have yet to get the bolt out of. Steve (CTR)

spray it a few times a day with PB Blaster rust breaker. In a day or two give it a whack with a BFH.   OR,  If you have an oxy acetylene torch, you can heat the pin till it's cherry red and let it cool down. Don't quench it with water. The pin will shrink when it cools and then you should be able to just tap it out.

The spacer is left over from the shock. It's likely rusted to the bolt (and the arm) as the bolt is rusted into the arm.

Corrected. See 11/21 post.

Ok.  So I'll try to attach pics.

The pin seems to have a he head on one end like a bolt rather than a nut... but on the other side looks like a built in spacer... where the damper mounts.

I looked at the new shock pin on host site and it looks like the spacer is built in but either end needs a nut... 

I'm still confused. 

Ps... yes its rusty... but that aside it looks like it shouldn't come out.

You should be able to knock out the pin. Rust usually freezes the pin to the arm.

May seem like an easy question, but how do remove the shock mount (pin?) from the end of the upper arm??

I'm rebuilding both, but one seems to have a bent shock mount.

It doesn't seem to make sense how I would replace this.

Cheers.

Rich