The first lot of HP engines (built in 1925 and loosely referred to as old HP) had dimensions closer to the BESA designs, with 16"x22" cylinders and 4' 9" coupled wheels. This particular engine is one from a latter batch (1948) with smaller coupled wheels (4' 3"), and with 15.5"x26" cylinders. 26" was the biggest stroke for any Medium Gauge Indian locomotive ever.
This locomotive had a large firebox grate area (31 sq.ft.), enabling burning of inferior quality coal.