Herb, if you look under the cover in front of the seat there is a U-joint there. If yours has the fan behind the U-joint, it might be too close to the long filter.
Go to NAPA and ask if there is a short filter that crosses with the 51410. That's where I buy mine.
The Sundstrand Type U hydro in the JD tractors has the fan on the rear of the hydro so there is no interference with the drive shaft. The fan also blows air across the finned aluminum half of the case, not the smooth cast iron of the front half. As a point of interest, the all cast iron (no fins) inline version of that hydro that is in my MF1655 did not have a fan at all for 10 years (1000 hours) and suffered no overheating issues in spite of mostly high pressure FEL work.
An option for you if the input shaft does not protrude from the rear of the hydro is to install a small oil cooler and electric fan in the return line for the hydraulic lift circuit. Then you can remove the OEM fan entirely and use the long filter if there is an interference problem.
TUDOR, Thanks for the help on the filter problem. I will check for interference as soon as I can get the tractor raised enough to crawl under it. The weather has not been cooperating lately. Spring is coming soon I hope. Been busy taking care of wife and doing household stuff. Herb
Finally, Got some warm weather yesterday and crawled under the Sunstar. It does have a fan behind the trans which will interfere with the longer filter. Looking at the fan the blades could be trimmed about 1/4" and then the longer filter could be used. Any thoughts about doing that? The fan would still be cooling a fair bit and the larger filter itself would have more exposure to air i addition to having more oil capacity.
I'm not sure if trimming the fan would make a difference. All I know for sure is that heat is the enemy of hydro systems. Most Sunstars came with a hydro cooler. I think I'd just get the OEM filter. They don't normally need to be changed very often.
The grass finally started to grow this week. Put down some Scotts weed and feed last week and it looks like it is working already. We had some rain last night and today the grass is jumping out of the ground. Will probably have to cut it next week. The mower is mounted and leveled and ready to go. The old Kohler is running O.K. but idling lousy. I did a rebuild but it didn't help. Just ordered a new carburetor today (An off-brand). We'll see how that does.