If your driveshaft is at risk of destruction with your setup you need a different driveshaft designed to handle your application.
I would not want the driveshaft to be a weak link or possible failure anywhere close to normal working range.
Here are some links to good driveshaft info
http://www.stovebolt.com/techtips/driveline/setup/index.html

After skimming through that you may determine you have a good shaft for the job, and if not I'd call a professional driveshaft shop and have one built pronto.

Grigg


•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-