One of the problems using pin dogs in a pine top is that the soft wood "wallows" out and the pins won't stay tight. This can be solved by drilling a 1" hole, gluing in a section of 1" hardwood dowel, and trimming it flat. Re-drill for the bench dog size.
You can also use a larger size (ie 1 1/4 or 1 3/8 ) and use a piece of hardwood mop handle which will work better.
If using a Borg or local builder supply 2 x lumber, I would go with SYP instead of SPF. This means you will probably have to go with 2 x 8s minimum and rip to the thickness. The SYP may harden enough (if it has enough resin in it) so you never need the inserts. The SPF will probably split or wallow out if you put much force on the bench dogs.
If using the plastic "pins" or dogs, the pine will probably work, or you can double layer some 3/4 cabinet ply. I have an old Workmate that has a single layer 3/4 Baltic Birch top (28 1/2" x 35 1/2") that has lasted me for over 15 years using the plastic dogs that came with it.
Go