Acording to Horizon the weights on the .91 and 1.00 are as follows:

.91 18.3 oz
1.00 20.8 oz

Both include the muffler.

That's a difference of 2.5 oz, considering the difference in power output the 1.00 simply smokes the .91. and the difference in weight is less than a pair of servos.

But to get back to the original question, yes the .50 will do the job but the airplane begs for the power of a 4 stroke plain and simple. Mine has a .72 on it and it flies fine and has plenty of pull out autority. I have seen a couple of them fly with .46's and the owners were not the least bit satisfied with them.