Check the casting numbers on the crankshaft itself. I believe that there are three different crankshafts for the 250 series. I see three completely differentmain bearing sets supplied for the various 250 S, SE crankshafts. The 280 S, SE used only one crankshaft, however it did use two different main bearing sets depending on the block style. None of the 280 series bearing sets are the same as the bearing sets for the 250 series. The latest version 250 crankshaft could be the same as a 280 but be sure to check the width of the thrust bearing on main journal #3 also check all the oil hole locations. The casting number on the crankshaft is the best way to be sure.
You probably can find someone on this site who has a good used 250 series crankshaft as an alternative.