micro vs. mini is a description of layout difference, not displacement. Therefore, you could have a micro that's a 270, 600, 1000, or 1200. They would all have the engine offset to the left, with driver's legs "straight" ahead. A mini would have the driver seated upright with inline engine, and could have a displacement of 600, 1000, or 1200 (never seen a 270 mini.) Many tracks, having little knowledge of the actual difference, use the terms interchangeably, but that doesn't make it accurate or right. Another key difference is rim diameter -- if it's a micro, it's a 10" diameter wheel like a 4-wheeler....Minis have 13" wheels. As far as driveline differences, both can have a direct chain drive to the rear axle, but micros have that chain on the left side outside cockpit, and minis often have it more internal. Some also use a driveshaft to a quickchange, almost like a mini midget setup.....speaking of which, in some places micros are called "micro midgets" (midwest) and the NMMA (National Micro Midget Assn.) is now defunct but used to hold a Nationals with several notable winners.
Hope that clears things up. And I wish tracks would bother to use accurate descriptions so it was more clear where each car was legal.