You sound like a lot of others here. The notion that ANY of us can read without assumptions is absurd.
I don't like OSAS. But it is simple that those to whom God has chosen to show mercy, the ones he made for the purpose of being with him in Heaven, WILL indeed be saved. If others "have faith" and lose it, or "have faith" and fall away, or "have faith" and for any other reason go to the LOF instead of Heaven, then their faith was not genuine, saving, faith.
But as I've responded 3 times now, I have made no statements as to your question of Simon and Peter. But if your "conundrum" is brought up for me to answer —not as a response to something someone said about Simon and Peter— that's different. I suppose, I will have to assume you are referring to Acts 8:9-24. I'm not sure why you think this should be a difficult passage for Calvinists. A Plain_Reading™ makes one wonder what was wrong with Simon, that he thought spiritual virtue or ability —specifically, 'the ability' to convey the Spirit of God being manipulated at will— could be bought with money. WHY do you insist (3 times now) that the Calvinist must jump to conclusions what was meant by 'believe' and by 'a heart not right'?
You need an answer? I'm not even a Calvinist, as such, anyway. But they (generally, since you group them all together) make a lot more sense to me than you do here. If Simon was of the Elect, he will go to Heaven. If not, he will go to the Other_Place™. But even if his belief was genuine, and certainly if it was not, he is more than capable of having a heart not fully understanding and not fully committed to God. Deceived. Addicted to money and false religion. There is no end to ignorant and deceived Elect. So are many of us here, and to some degree, ALL of us. Yes, that includes me, and you.