Doing an Oblivion and a Morrowind play through after a long time to psych myself up for Skyrim. I have enchantments that boost my block up past 75, but I haven't gotten the prompt telling me about the enhancements.

I completely forgot, but don't you get a shield bash technique at 75 block ability? How do you do that move?

Most mastery perks ( there are exceptions ) are not given with enchantment or spell boosts, you need a natural skill of 75 to get the bash ability. You don't perform the move, every time you block there is a small chance of it activating.