 It differed from its predecessor mainly by having a wider choice of engines, along with a new nose moulding giving it a more bulbous look and a grille to cool the new front-mounted radiator, and a revised rear end with new lights and a different engine door.The Mark I Leyland Nationals had an 8.3-litre straight-six turbocharged Leyland 510 headless diesel engine.The Leyland 510 engine had an unusual design, in that it featured non-detachable cylinder heads; any work on the valves required the crankshaft and pistons to be removed to enable access from the cylinder bore.