Ah, domestic. I had figured you were going international which would allow you to use the Ambassador Club. Unfortunately domestic 1st won't get you in. With the short connect time you may have a bit of a hike between planes depending on where you come in to STL, either the C or D concourse.
It appears your flight leaves PDX at 615am, I would get to the airport by 515. You arrive STL at 1206 and connect to the MCO flight leaving at 135pm. That is plenty of connect time. The MCO flights are always crowded, but maybe in these new times it won't be so. Please let us know what you find.