727 yoke wont come out. What's the trick ?

If you swap the output shaft (and I would) make sure and use the correct output shaft to match the front planetary gear set your using. A 66-75 output shaft with a slip yoke is the one that you need if you use the planetary gear sets from the motorhome. You can't tell the difference with the naked eye but the front splines on the output shaft are cut at a slightly different angle on the different year spans so you have to use the matching vintage front planetary gearset for the output shaft. If your not sure what year the output shafts you have are here's a picture to identify them