You'll need to preserve the current ratio of front to rear (rolling circumference).
I have a 1602D, and here is what I did, i purchased a cheap set of John Deere Turfs with rims (rears) brand new on Ebay. I measured my ratio prior to mounting, then I had a wheel spacer/adapter made to match the bolt circle on the JDs with the Yanmar bolt circle (this it the biggest problem). Once the spacer was installed, I measured the rolling circum, of the rears, calculated what the fronts should be and found an appropriate tire (Carlisle....), i then found a JD rim that would fit my fronts and the tires and purchased those.
A little work, but they work great. I then had them loaded with CaCl and have never looked back, the best upgrade I have done to my tractor.
Cheers,
Rob