Bernie, if you have the tools and the time, and are fairly mechanically inclined, then you can probably handle this task at home.
The cast iron Dana 20 and three speed tranny are fairly heavy and are tough to move around while working on your back on the floor, this would be a two man job.
If you separate the tranny from the t/case on this truck there are two things to watch for...
1) if you split them at the adaptor in front of the t/case, the bearings that support the input shaft will probably fall into the t/case....
2) if you split the adaptor off the tranny, you MUST lock the tranny into first gear or you may drop the input bearings into the tranny (requiring a partial teardown/ rebuild)
When removing the tranny, leave the bellhousing on the back of the block, it will make removal much easier.
Good luck.