My thoughts too!Nice find! You might want to clean the rams up on those cylinders and just use them. A little oil seepage is a cheaper than new cylinders. Especially if the blade is not used a lot.
A 400 blade mount will work on a 420 and 430, I have one on my 420.That’s probably the reason the mount was removed, someone tried to fit to a different JD. The 400 GT had a mounting system not compatible with any other JD.