sentences:  In 1972, the Detroit Diesel 12V71 became available as an option; though rarely ordered, the V12 engine would remain through 1978.Although Detroit Diesel had developed a gas-turbine version of the GMC Astro in the early 1970s, fuel-economy concerns would keep it out of production.In 1977, the Cummins KT450 and Caterpillar 3406 became options; the larger engines required the addition of a larger radiator.