The term your looking for is the engine dimensions.
The problem is that there are many different dimensions associated with a motor. There's the cylinder dimensions, placement, and angle. the spark plug placement, angle, and dimensions, the crankcase dimension, the carb placement & dimensions, and the exhaust/pipe/muffler placement & dimensions.
If you locate these measurements, they're normally in the form of engineering outline drawings, viewed from two more angles. For instance, attached is the outline drawing for the Franco Morini S6-E engine