It is a '66 with the Spicer FDS750 front axle and Rockwell H131 rear, powered by a poly 318 with a 4 spd transmission that has dual PTO ports. I believe it was in '74 they replaced these with the W600 which still had the Rockwell rear, but replaced the front with a beefed Dana 70. The W300 series trucks had the Dana 70 axles front and rear. I also have a '72 W200 with a Dana 70 front and a 60 rear from the factory, that is powered by an LA 318 driven through a NP 435 to a divorced NP 205. The W500 has less than 25,000 original miles and the W200 has less than 19,000.