Instead of blocks run a 2x4 and a 2x6 all the way down and you have the same as a notched 5 1/2 x 5 1/2 and bolts yes .
Instead of blocks run a 2x4 and a 2x6 all the way down and you have the same as a notched 5 1/2 x 5 1/2 and bolts yes .I like to extend the 4x4 posts to be used as rail supports to reduce lumber and hardware. It is allowed to use carriage bolts and cleats along with some extra screws to support the rim frame?