V engines have matching cylinder pairs from each bank mounted to the same pin on the crankshaft. This means that first one cylinder hits top dead center, then the next. (the Ferrari Testarossa was a 180deg V12)
Boxer engines have the connecting rods connected to separate pins on the crank, so that the pairs of cylinders are always moving in opposite directions (they both move out together, then back in). (a Subaru is a horizontally opposed boxer engine)
Shamelessly paraphrased from
Introduction to Internal Combustion Engines by Richard Stone and Internal Combustion Engine in Theory and Practice: Vol. 2 by Charles Fayette Taylor, that I have on my bookshelf
Not sure what a Flavia or Gamma is.