How can I put this any clearer than that?

BME 44 and BME 50 have the same mounting dimensions.

I did the same switch on the same plane you wanna do and it was
an unbolt and bolt back in affair.

That's all you need to know. I guess it's hard to trust a stranger but I'd say it anyway: TRUST ME ON THIS!! :-)

On the other issues about weight and if it's the same engine or not I think Dave stated the obvious: They are different engines [X(] One is a 44cc
and the other a 50cc engine.
Other than that they mount the same, the carb and the throttle arm
is on the same position (you won't need to do any mods on your throttle servo/linkage) and the prop bolts the same way.
I don't remember If I had to slide the engine back or forth on the mount but if I did It was certainly very very slight. The whole switch took me about 10 minutes. Ok.. call me slow

The 50 is about 6ozs heavier with pits muffler and ignition included.
I did the comparison on my digital food scale while I was doing the switch.

I hope this helps,

Stratos.-