As for you last picture and whether you need a undo that pin.NO you don't,that is just a pin to hold the front roller on.The only way to remove it is to cut it off,but once its off it won't go back on,unless welded,so unless it is very worn then just leave it there.
Sounds like you have gone to far to soon and now you got yourself all flustered.That happens.
I think there was too much focus on the height adjuster there not that hard to adjust.The first picture CyberJack put up on the right is the height adjuster you can see the teeth and the different settings to where the front roller sits(Inside the red circle in the picture below).Also there is another adjuster near the blades but too late now.
Also there (In the green circle) is the non-removable pin for the roller in your last picture.
[Linked Image]

I guess the thing that faces you now,is.
Is it worth your time to do?
Do you want to do it?
Do you want to learn about?
If you wanted to restore it your now in the right spot to do so.
It all depends on what you want to do.If you think it's done then it's done.No good listen to other people and you will get mixed answers as some will be on either side of the fence.
The big question is.....What do you want to do?
The only manual I can see there and find is an owners manual so don't get dis-guarded by that you need a workshop manual and I'm not sure anybody would have one.
So just ask your self,
Do you want to do it?

Here for a good time,not a long time.