The Farish model represents the earlier version, built up to the early 1970s, whereas the N Gauge Society kit is the later 1980s build. These have welded side uprights, different bogies, higher end handrails and various other detail differences. The two types are/were seen together in the same trains too. The NGS also did an etched brass kit for the earlier type (actually for the SR Walrus version with optional parts to update to the Sealion) but not only was it actually 2mm scale (reduced down from a 4mm kit) but a LOT of work to build.