I agree with LI, what you have here looks like a 5D ell with some tangent length added for the flange.
I cant find a cut sheet on 5D cast iron ells, but Gruvlok 5D ells have a 36" (914mm) center to end, 6D Gruvlok ells are 42" C/E and a 4" 5D Gruvlok ell is 24" C/E so it looks suspiciously like 1D is added to the nominal radius to get the 90 deg C/E. This is probably some dimensional standard that comes from older iron fittings. The center to end of a 60 deg 5D Gruvlok elbow is 23.25" (~590mm), does that jive?
Odd way to call it out based on the C/E of the 90 degree bend instead of just marking it 5D but I suppose when tangents are added by default its not as easy as calling out the radius.