John Deere 730
This green machine from 1960 uses an engine with just two cylinders, but there are 376 ci (6.2L) of displacement inside. The giant bore is 6.125 inches with a long stroke of 6.375 inches. The lack of engine material helps make the 730 the lightest of this bunch at 6,790 pounds. In a test of the previous model (720), the same engine was capable of producing 59 hp at 1,125 rpm. There were 30,000 of these tractors built from 1958-'61, including gasoline, propane, and all-fuel versions. When new, this '60 sold for just $3,700.
Caterpillar D2
The four-cylinder D2 was built from 1938-'57. This particular tractor was made in 1947 at the Peoria, Illinois, plant. It has a displacement of 221 ci (3.6L) and is able to make 125 lb-ft of torque at just 1,050 rpm. The muscle was rated at 42 low-end horsepower. In the same test, it scored a maximum pull rating of 7,413 pounds. The 50-inch tracks help make this crawler very capable in rough terrains.