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The term is Spar Yarder. The idea is to drive the chassis as high up the hill as possible. Set the anchor cables and deadfulls. Then rotate and raise the mast. Run a very long overhead cable to somewhere near the bottom and tension it almost straight. There is a cab for the operator who winches logs up the hill to a landing where an loader puts the logs on trucks. The dangerous job is down on the hillside where men in helmets and spikey boots set choker cables and dodge runaways. The Madill company in Nanaimo, BC that did hundreds of conversions. If you search the heavy equipment auctions there are almost always a few on offer.

A second company that use Sherman chassis' for rough terrain use is Finning. Put a big air compresser on one end and a very powerful rock drill hanging off the nose. The companies use these to drill deep holes for blasting hard rock on construction projects.