I did some research on the whole angle block thing - your new blocks should be the same angle as your old ones. If they are parallel make your new ones the same. The only time you have to introduce an angled block is if you have created an angle (say by adding an extended shackle). The pinion shaft should be parallel to the transmission output shaft.
Interesting. Here are my thoughts on this. Take them for what they are worth and please don't take this as me trying to start an argument or anything. Just having a friendly conversation.
Back in the day, we used to tip the axle up a little in the pulling trucks to straighten the driveline as much as possible to take the twisting strain out of the u-joint. Granted that's an extreme case but to my recollection, we never broke a universal joint either.
In my mind, the worst that could happen is either it causes a vibration or wipe out the rear u-joint faster. The axle twists up (axle wrap) under acceleration and the angle changes with load as well so that dimension of movement has to be accounted for by the universal joint. The same thing with your brush hog analogy. Most people run a chain for the third link so that if you hit something and the mower jumps up in the air it doesn't bend anything. It also causes a change in driveline angle of the gear case relative to the pto. I don't think it's necessarily a requirement that the gear case is parallel to the pto but most implements are designed that way probably out of convenience.
The only question in my mind really with the angled block is will it cause some weird vibration as the axle travels. Hopefully I will find that out later this fall. The only other possible problem I can see is keeping grease to the pinion bearing but I think the angle is small enough that won't be an issue either given the height of the fill plug.
Sorry for the detour Greg.