Welcome to the L200 club! Parts manuals are easy to come by online. I have a couple of .pdf versions. If I recall correctly, the Messicks one is the highest resolution that I've found, about 5.6 Mb for the entire parts manual. You can download it piece by piece here:
You can also order hard-copy manuals online, like the Messicks ones here:
I have a hard-copy of the user's manual at home, but no digital version. I do have the ability to scan it, though... so if you're interested, let me know. I don't own the service manual, but I would like to.
Keep in mind the L200 and L210 are virtually the same tractor... from what I have gathered, the L200 was the first Kubota legally imported into the USA, (around 1969) and was sold in both Japan and the USA... where the L210 was made for the USA and not sold in Japan. The sheet metal on the L210 is different, the lights are on the hood. I read all this somewhere along the way, after I bought my L200 last fall.
My L200 has the wrong air intake as well! You can try some of the tractor junkyard sites, there's a big one in Kentucky, that I've seen online. Sorry I can't help on the hour meter, I haven't had to mess with that on mine, it works fine.
As far as the finish mower... I don't think the brand of mower matters, the L200 has the standard USA rotation on the PTO, so any Cat 1 PTO mower should work for you, just keep in mind the hp rating - the L200 is only about 15hp at the PTO:
So with the L200 you're on the lower end of the HP rating for a 5' mower, you'd probably want to go with a 4' mower instead of a 5'... see the chart at the bottom:
That being said, my L200 came with a Rankin brush hog and it works fine. I should measure how wide it is. I haven't tried it in super tall hay, (if I did, I would take it slow) but I've mowed a bit with it and it works.
Let us know what you learn!