Can rough but beams be sanded down at one spot to fit strong ties?

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My plans called for 6x6 post to connect to 6x8 beams via post to beam Simpson connectors . I had to go with a rough cut saw mill to cut the 6x8 beams because no lumber yards carried it 16 ft long. That leaves me with a 5.5 sanded post to 6 inch rough cut lumber beam. I called Simpson and they said it was a special order bracket because it has to be custom made, probably around $100 a piece. My question is , would it be okay to take a sander or plainer and take off a 1/4 inch off each side of ...