2 and 3 cylinder engines can come from heavy equipment, such as bulldozers, loaders, or generators. 4 cylinder Detroits can come from heavy equipment as well, but were also installed in busses and medium duty trucks in the 1950's, 1960's, and 1970's. They can be had for relatively little money(under $1200) and parts will be made for decades to come (because of foreign popularity).
The 71 Series was introduced in 1937 and produced into the 1990's. The 53 series began production in the late 1950's. Detroit also made a 92 Series, a 110 Series, and a 149 Series.
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