From the listing for this 1970’s McLaren F1 Car for sale:

The McLaren M29 was designed by Gordon Cuppuck to replace the large and unwieldy M28. Abandoning the previous car’s honeycomb monocque construction Cuppuck reverted to double skinned alminium sheet and pushed the cockpit well forward to enable the use of a single large fuel tank between the driver and the Cosworth DFV engine. This allowed the car to be slimmer and lighter with more efficient ground effects and improved the aerodynamics of the bodywork.

Introduced at the British Grand Prix in 1979 the M29 was qualified in 7th by John Watson who then finished a very competitive 4th, McLaren’s best result for some time. M29-2 was driven by Patrick Tambay for the remainder of the ’79 season, he was quick but did not have a lot of luck usually being the victim of engine failure.

Over the winter the M29s were upgraded to C spec and John Watson took M29C-2 as his race car for the 1980 season using it for all the Grands Prix that year.