Scooterbug;
I will attemt to answer your question, however I am not certain if you mean the shims that are located at the outside top of the front axel spindle (king pin). If you mean shims inside the gear cases to shim the proper clearance of mesh of the king pin bevel gear with the axel bevel gear that is another matter. I have rebuilt the front axel gear cases and spindle/king pins on my 1300D which are very similar to yours.
Does your lower gear case have an oil seal or oil O rings, and does your spindle/kingpin have a cross bolt through the knuckle arm (at top) or does the spindle/king pin have a threaded portion on top where a nut screws down on the top of the knuckle arm? The later model gear cases and spindle/king pin with the oil seals, ball bearings in lieu of king pin bushings and screw on top nut are much more rugged than what I have on my 1300D
First, let me say that taking the advice of Danny Parker ( who has responded to your question) is very wise. I have bought parts and equipment for my 1300D, including rebuilding my engine and he is straight on, honest and very knowledgeable.
If you mean the shims at the top of the spindle/king pin, yes they are usually necessary to pull the lower gear case up into the upper gear case properly. on my 1300D I made shims on my lathe for the this purpose and decided that I wanted to have about .005" clearance between the upper and lower gear case---just enough clearance that you can just feel the lower gear case move as you pull up on the top of the spindle/king pin with the knuckle arm attached to top of spindle/king pin with the top nut tightened. If you have minimum clearance without the shims, then you do not need any more shims. NOTE: I have a Yanmar factory original 135(D) 155(D) Service Manual and it states that you should have .004" clearance instead of my .005" clearance. I was lucky to find an orignal manual on e-Bay, as the one I bought from Hoye was a poor reprint--poor as to the photos. If you do not have a service manual, but the one from Hoye anyway. It is 80% as good as an orignal.
Now, concerning shims inside the gear cases. Do you mean shims that will shim the lower gear case bevel gear up to the axel gear (here again minimum clearance)? It is likely you will not need them when you have the spindle/king pin shimed as I have described in the paragraph above( this may not be true is some yahoo mechanic before you has been into the gear cases and left the shims out-if any were there originally from factory) You can check to see if you need shims on the top or bottom of the lower case bevel gear by assembling and tightening the upper/lower gear cases and top spindle/king pin nut, as I have described in the paragraph above and then with your had check that the front axel stub shaft has a bit of "free travel" as you rotate it to the right and left. In other words you are checking to see if the there is gear tooth clearance between the gear teeth of the stub axel bevel gear and the lower case bevel gear. It is a big problem not to have clearance, not so bit if you have too much. If you have not ever worked with gears before, then what I say about feel, will maybe be a bit foreign to you.
However, since you specifically mentioned 1mm shims, I think you are talking about the upper shims on top of the upper gear case. Those shims originally came in 0.1mm (.004") and 0.3 (.012") mm sizes. (There should be one or more 1mm(.039") spacers on top of the upper gear case spindle/king pin--its size is 22.5mm ID x 40mm OD x 1mm thick) Are these 1mm spacers what you are asking about? On my 1300D I needed several shims and spacers as the top of the upper gear case had worn in the 30 year life of my tractor.
I hope this helps you.
. Bob