reman vs new
New: has a good warranty, through the manufacturer, is installed by trained technicians. If you had a problem, you know where to go, and you know that they're using OEM stuff and you know Kubota is who made it, who trained the guys who put it on, who trained the parts people to order it, etc. IIRC they are 1 year warranty if installed at a Kubota dealer, and with that we also have to consider the emissions equipment. A brand new engine is already set up for your particular tractor, and it's emissions equipment.
Reman. You pull the engine, normally then have to pull the head and re-use it (or replace if it's broke/damaged) for a short block. Then reassemble. These tractors are NOT easy to work on, either. Might have 90 days warranty? Depends on the remanufacturing facility. And even then, what stipulations are required to keep that warranty? Look into it closely most of the time they use manufacturer's warranty so if they replace a rod and use an aftermarket one, the warranty on that part is through the rod's manufacturer which might be 7 minutes or it might be none at all or it might be 135.25 days. Who knows? That's why I said look closely at that. On emissions, it's not uncommon for reman builders to mix and match parts that they think (or have read) will work. They might use a head from a V2403-T on a V2403CR for instance and there are differences, such that they'll cause problems in a lot of ways-one of which is that it won't meet emissions requirements.
Repair. You take it off of the frame, totally disassemble, measure, pay to have it machined, checked, repaired, then you reassemble. Or pay a shop to do it. If you pay a shop, you're out labor + parts, and likely the labor to R&R the engine assembly (which in itself is intensive). The warranty on this type is parts only, usually 90 days. Labor is on you should there be an issue. And again, these particular tractors are labor intensive meaning lots of downtime.
Lots of options and lots to think about. Remember that price alone isn't always the more important aspect.