There was an Evo .40 for a while...haven't seen it advertised lately though.
The engine that comes in an Alpha and X-tra Easy 2 is the .455 with the lower case a (looks almost like an @ without the "tail" ) on the head and below the exh. port.

I think the .40 was dis-continued for the .36?

I had an Alpha engine and a .46NT dis-assembled right next to it, (put bearings in both of them ) just last week, the .46's piston being smaller in bore (a few thousandths) The only real, measurable differance was the stroke of the crank.

IIRC the Alpha .455 TPS came out first installed in the Alpha trainer ...then the .40 and .46 were introduced simultaneously some months later...and somewhere in between the TPS "Alpha" engine/3 blade paddle prop/flywheel/spinner was made available as a unit (sold seperately from the trainer )