Mr Webb built a simple 0-8-0 locomotive having 240 litre cylinder volume and a three cylinder compound with 320 litre.The compound was better and more were built and hauled coal for many years. The first P2 with 220 psi had 445 litre and a 250 psi version can thus have 395 litre for same tractive effort. A Webberized version shall thus have 33% more that is 525 litre. If we allow GWR strokes of 30 inch we shall have two external high-pressure cylinders of 15 inch diameter and a single inside of 30 inch. Two 15 inch cylinders can evidently be further apart than the 21 inch cylinders of the first P2 for a given loading gauge. It will also allow plus-minus one inch horizontal movement of first coupled axle giving less track stress.