I'm not familiar with the Long engine. But if you can pull the pan off, on most engines you can usually roll a set of main bearings in quite cheaply and easily with the pan off, without having to drop the crank or split the tractor: Unbolt the lower main caps, roll the top half of the main bearings around the crank and out (make sure you roll it out the correct way - most mains & rod bearings have a little 'wedge' on them to prevent them spinning in their bore and will thus only roll out one way). Roll new top halves in. Replace bottom halves in caps and bolt back together (being sure to centre bottom cap). Since you have the rods out, you'd do the rod bearings & wrist-pin bushings when you have them out. Proper practice is to gauge and check them and the crank to see if a grind & oversized set is need. But even if you just put another standard set in with nothing else done, you'll have given it a little fresh life cheaply and easily. A couple of small brass punches and a good strip of nylon/UHMW to help rolling them out around the crank is usually all you need.
It's definitely not a 'proper' rebuild by any stretch and is rather quick/dirty. But as long as you can get the pan off, for the cheap cost of a bearing set I'd definitely be doing them (assuming I didn't want to put the time/money into a full rebuild). I wouldn't want to do a ring/top-end job and then have a pile more compression going into the same old/worn rod and main bearings.
I'd also recommend sending the head off for a valve job (be sure you send it somewhere that knows the importance of valve protrusion). But if you're really trying to do things quick/cheap, I suppose a thorough inspection of the head & valves and then perhaps putting it back on as-is might be ok. I'd definitely be spending the few hundred $$ while I had it apart to get the head properly gone over, but that's your choice.
This chap (link below) specializes in parts for imports tractors from that era. I've bought a few things from him. He's a bit of an odd duck, but he knows all the import tractors from that era every well and stocks lots of parts:
New replacement parts for Fiat Oliver, Cockshutt, Minneapolis Moline, 1250, 1250-A, 1250A, 1255, 1265, 1355, 1365, 1450, 1465 tractors
www.importtractorparts.net