Here's all the info (manuals) you should need to figure this out for yourself:
http://www.stovebolt.com/techtips/driveline/setup/index.htmlA few things to consider:
Adding the extra transmission length changes the geometry of the shafts after it, you need to check and adjust according to the driveline manuals in the above tech tip.
Adding the OD will spin the driveshaft faster, can it take the extra speed? Double check the critical speed for that size and length shaft, this is in the applications guidelines manual.
If you lengthen a shaft ensure that the drive line will safely and reliably do what you ask of it.
I don't have a real answer to your questions other than please do your homework on drivelines first.
Then you may be better prepared to ask and understand questions and answers from gear vendors and your driveline shop. The manuals will also help you to implement the solutions, probably even solve your own problems/questions.
I know when I started on my truck I knew next to nothing about drivelines and how they were supposed to work and what to consider. But after finding and reading the manuals I had a good time measuring, designing, ordering, installing and double checking the two piece driveshaft in my truck.
You can even find and download the Spicer driveshaft components catalogs and pick and choose the parts you need from what's available.
Grigg