As you are well aware there is no ALL balls swing arm kit for the Pe 250 - 400 1980 - 1981 model
So I purchased a Rm 250 79-80 kit and modified it to fit at a fraction of what It would cost using S.G.Parts. The kit centre shaft is 7.5 mmm shorter ( 192.5mm ) but this not a problem as you cut it in half with a S/steel cut off wheel , clean up the cut edges and make sure they are square .
Next get the old spacer and cut it to make up the right length ( 200mm)
Assemble with short piece in the centre .... the rest is as per normal