The top needs a 1×10 perimeter frame…. I was going to try using a Lock Miter bit I have, but couldn’t get a tight fit and the end grain locking tab kept braking. So I decided to glue and screw a simple but joint…
to support the frame, I cut a shelves on the outer sides of the post tops. I cut the cheeks on the band saw and for the shoulders I set the depths stop on my SCMS and used the fence stop to get identical parts.
A little paring with a 3” timber framing chisel used like a slick
All cleaned up and spiffy….
-- Pine is fine, but Oak's no joke!