DBGT-
The Ford/Accufab question has been debated adnausum. Check the multiple previous threads. Bottom line both kits will WORK FINE. Like Mike says, if you are comfortable with a Ford dealer who has a tech who can change out the bolts to your satisfaction, do it! If not get the bolt kit free from Ford with your GT VIN and have a person of your choosing install the kit. Or buy the Accufab kit and have it installed by your preferred installer. Either way the problem is solved.
Actually nota4re has a pretty good explanation of torque-to-yield (TTY) bolts but let me amplify a bit on several of his points. Typical engineering practice is to design a bolted flange with as high a bolt preload as possible based on the bolt material. Typical recommendations are a bolt proof load equal to 90% of the material yield strength. Varying amounts of thread friction which can vary SIGNIFICANTLY by non-use of any lubricants (dry threads) or the use of engine oil, mouse milk, never-seize etc. can significantly alter the bolt load. Thus it it important to follow any factory assembly instructions carefully.
Thus if we design a bolt load to equal 90% of its yield strength (based on bolt tensile area) the bolt will never take a permenent "stretch". Measure the bolt length, install, torque to whatever torque value specified to take the bolt to 90% yield, untorque the the fastener and measure. The bolt will be identical in length as before the install. This is because the bolt was never loaded above its material yield point. This is true for the first torquing or multiple torquings thereafter.
I agree with nota4re, what we REALLY want to know is bolt STRETCH, but this is very difficult to measure instu. About the only application where you can easly measure this stretch is a rod bolt and there are instruments available to make this measurement. Since most applications cannot measure stretch directly we assume a thread friction (which varies with lubricant used) and calculate a bolt load.
When you torque a bolt above the material yield point (ie TTY bolts) you enter a portion of the material stress-strain curve that is not linear (meaning a given strain or bolt stretch no longer returns a linear amount of material stress or load) and the bolt load produced for a torque above yield is even less reliable at predicting actual load developed by the fastener. For this reason, torquing specs in this plastic/non-linear region of the bolt material strength are usually specified as an initial amount of torque to take the load up to near yield and then an additional angle-of-turn afterward to load the bolt into the non-linear bolt strength region.
It was stated, and is true, the six Accufab outer diameter fasteners on our rear axle half shafts come with standard torque callouts (resulting in below material yield stress) whereas the Ford specified bolts are TTY. My preference for this bolted assembly is the TTY bolt as for a given bolt size a higher preload can be achieved with a TTY fastener. Again though, both kits will adequately address the previous inner bolt failures.
Hope this was not too technical and helped in understanding.