Proper subfloor for hardwood in a renovation
I would not install the hardwood flooring directly to the 3/4" sub flooring. (BTW at just 3/4" thickness that subfloor is made of boards and not planks as you indicate). A board subfloor is not, in my opinion, sturdy enough to result in a solid floor nor does it provide a decent hold for the flooring nails. 

Even if the subfloor was satisfactory you do not want to lay down the new flooring in the same direction as the subfloor. One particular reason being is that any changes in those subfloor boards (cupping) will telegraph right through to the new flooring boards above. Another reason is that a nail row for the parallel flooring can land right on the space between the subfloor boards and have virtually no retention.

You did not indicate how thick your new hardwood flooring will be but if it is some of the newfangled type of engineered material that is not very thick you have all the more reason to not install directly on that board subfloor. 

I installed 3/4" tongue and groove hardwood flooring on top of quality 5/8" plywood that was in turn installed over 1 1/2" tongue and groove subfloor planking. The plywood was screwed down using decking screws every 5 inches across the sheets and every 4 inches at the seams. The hardwood flooring was fastened down with hardened spiral flooring nails that were 2" long and pre-drilled through the tongue entry of the flooring. The result was an very solid floor that has no squeaks even after going on 7 years.