OK, and the answer is.... A home made full-time 4wd conversion for the Dana 18. My Dad never liked that being in 4wd causes slippage around corners. Especially in slick conditions. So... he took machine shop night classes at the local community college and built his own center differential conversion from scratch. It's been in the Jeep and functioning for 40+ years now. It's very clever. High and low range still work and the 2wd/4wd lever locks the center diff. Here's a drawing of a stock Dana 18 (I apologize for the quality, the paper copy hasn't survived well): And here's the full time setup (which thankfully has survived much better): The basic rundown: He used a piece of pipe for the housing. He made a cap for the housing that has bearings for the new output shaft and the new differential case. He machined a custom differential case that replaces the rear output shaft in the lower part of the Dana 18. It still uses the stock low range slider gear and 2wd/4wd shift collar. The spiders are Dana 25 parts. He made a custom cutter for machining the spherical pockets. The front output shaft spider gear has a smaller hole because of shaft size limitations. He initially made a sleave, splined inside and out to take up the space but it didn't hold up. He then had a machine shop weld up the gear and cut new splines from scratch. He made a custom rear output shaft, but used the standard output housing, speedometer gear and yoke. As noted before, the custom front output shaft needed to be small, but has held up well. Realistically, it should. The jeep has 4.88 gears and the same Dana 25 parts in the axles. That means these components in the transfer case will only see about 1/5th the torque that would break an axle first. The 2wd/4wd shift collar works as it did before, but now it locks the front output to the differential case for locked 4wd. He made it so no modifications were done to the Dana 18. He was worried it would break and wanted the ability to put the Jeep back to normal quickly. With the CV joints in the front axle and the center diff, it's always in 4wd and drives fantastic in slick conditions. Just like a Subaru. It's also surprising how little you need to lock the center diff when offroading. He said you're all free to use his plans royalty free if you want to make your own. ....and the box on the front axle was an attempt at locking differentials back in the 70s. It worked similar to the diff lock above. He extended the splines on the left axle shaft and had a cable actuated collar with internal splines and a dog clutch on the end. He cut a matching dog clutch into the end of the differential case for the collar to lock into. He tried it once in the back yard on wet grass and it took the dogs right off the differential case. He though about having a hardened sleeve welded into the case and using more and finer dog teeth, but never got around to it. Neat idea though! Well, that sums up the build. Hope you enjoyed it. It's a pretty neat old Jeep that got a lot of Jeeping use in the 70's and lots of tractor use ever since. Even though it's low and has open diffs, it always did well on the trails. With the tires aired down, it's flexy enough that it always seems to have all 4 tires on the ground. Of course, nobody was doing modern style rock crawling on the Pacific Northwest trails back in the 70s. I'll try to get some under hood pictures when I'm out visiting in the late spring.