Look in
Machinery's Handbook under "fits, running". Stephenson valve gear wants to err on the loose side even when new, so an RC 9 fit is in order for these very large bearings. RC 9 equals .025 to .051 of clearance for diameters ranging between 15.75" to 19.69". The RC table is really a very loose guide, but it's better than nothing. IIRC, we have aimed for .040 clearance for eccentrics about in that size range.