Ryan,
I believe the 1863's had the hydrogear hydros in them. I haven't heard anything good about these hydros. The 1864 had the Sundstrand hydro and we all know how bullet proof they are. Not to say it's a bad tractor or anything, but take that into consideration. Some guys have prolly run the tires off a 1863 without any problems. Good luck and keep us posted.
Under edit: The 1864 has powersteering also and the 1863 doesn't IIRC, otherwise identical.