I don't think anyone has ever needed new shoes the first time they are worked on. There are several things in there that can be reversed for a new working surface, including the shoes themselves, good for another 25 years.
Talked to a clutch builder and they can do it cheap.
Norm , I have had this tractor 5yrs and i think from working on it and the condition it is in it came over here as a whole ,So many bolts are rusted together and parts that look like they never have been apart . When i bought it the brakes didnt work and were full of water.I live on flat ground so brakes were not that big a deal. The shoes are worn all the way as in gone.
So you have inspected them....I have read of dozens of cases over the years where guys ordered the $160 set of brakeshoes, only, after inspection, to find out they weren't needed.
I'm not familiar with the Yanmar brakes, but take your drums to the brake guy too. He can cut them and then custom build the shoes to match the cut. Let's you get some more life out of the drums and a thicker shoe to boot. This is something that they wouldn't even charge you for (other than cutting the drums).