Where have you found the 27 spline d-30 Longfield cv shafts. I know they make them for the TJ rubicon D-44 setup. I checked their site, and they have a 27 spline axle, are these what you are talking about for a d-30?
I will agree the shaft will not brake, and it will probly twist the splines before it breaks. In my oppinoin the weak link would be the ring gear. Running these shafts would be similar to running the 30 spline upgrade or CTM ujoints on cromo 27 spline shafts. But with a good stiff diff cover, I think you are running a ruff stuff cover GOOD, and either a truss or an axle sleeve of some sort. This will hold up your 35 BFG tires with an aussie.
As far as the machining, I think with some carefull planing you could do it yourself, with a dremel and an angle grinder. All you need to do is clearence all three unit bearing monting holes. I have seen the sfafts installed with out the maching temporaraly, but you would not be able to turn, but you could take measurments.
I am planning on running a smilar setup on my 30, I have pieces laying to sleeve mine, truss it. I have a ridder cover, and plan on an aussie as well. I like the idea of the cv shafts because they do away with the ujoint problem, and allow a higher angle of turning before they bind, lessening the stress on the joint. Although I have kinda had my heart set on some cromo shafts and CTM ujoints. Both probly run the same price.
Micah