I would consider,,with a 3 piece head spreader bar,,as you shorten your lengths,,and the reason for taking out the 4" extension is to make the head spreader bar a 2 piece and much stronger. At 3 piece,,there is a ton of stress put on it by shortening the dogbones and more percentages of failure over time. Just my 2 cents and I know of one newbie user that already bent his head spreader bar. Good luck and post your testings.
Now you have me digging out my shortened pieces of amsteel and testing again,,,darn!