I'd personally do different additions, separate. But those two will be good together. It's what I've got planned for a DIPA that started at 1.085 and it's down at 1.014 now.
I'd do Amarillo first for 7 days, pull it, and add Simcoe for 7. Then package it immediately. Layers it a bit. I did that last time for my IPA, and did it again for a DIPA I did. Sometimes I toss it all in the keg and dryhop while I carb, but I really like nabbing one layer and tossing another fresh burst in there before I keg it. It prolongs it all I think.