Wood bed rails - lumber and dimension advice?

I'm making a set of bed rails to convert the head-board and foot-board of a crib into a full size bed (to avoid buying the $200 conversion kit). I have the 'claws' to attach to the ends of the rails and engage with the head-board and foot-board. I also have a rigid box spring to extend between the rails, so I don't necessarily need slats.

I'm looking for recommendations on the lumber type and dimensions of the two rails? The span (length) is roughly 76" and the rails will eventually be painted.

I'm trying to balance cost v. over-engineering it. I believe 1"x6" oak should be sufficient for the weight, but is it overkill? I could also use 2"x6" (or 8") framing lumber I believe. Any thoughts are welcome.

 

If painting then oak is not needed,

1x6 pine would be a good choice with a 1x4 on the inside to hold slats or the box .