Made by Yanmar of Japan for Deere in early/mid 80's.
3cyl yanmar
18hp @the pto.
8spd forward 2spd reverse
4wd version weighs approx. 2000lb.
The 50series was JD's first entry into the compact tractor class and they are darn near indestructable.
Value is around $4k-$5k depending on region and accessories.