I've been reading up on harnesses and found this... If you've already seen this... good... if not, please read this article and take a look at the recommendations from Sparco (the TRW harness) on how to install, wear, and care for a harness...if you are going to do it... do it right or stick to your 3pt factory seatbelt please for your own sake.
I've taken a course in Vehicle Crash Dynamics and you'd be surprised at how high the forces really are... even if you already thought they were high...
http://www.solo2.org/blogs/spe....aspx
http://www.sparcousa.com/pharness_comp.asp?id=234