Giving the Royal Navy later warship designs in 1750

What if the Royal Navy in 1750 replaced its first rates with Victory, second rates with London-class ships, third rates with Africa and frigates with Constitution-type ships?

The first and second rates would fare well and the frigates would become very powerful, though Africa-type third rates would be comparatively light in firepower and the expense would be substantial.

The imagined replacement affects each rating differently. Victory and London-type ships are judged satisfactory choices for the upper rates, while Africa provides a capable but relatively lightly armed third rate. Replacing both fifth and sixth rates with Constitution-type frigates would create a much stronger cruising force. That strength comes with a large bill for the Royal Navy. The stronger fleet is expected to leave France at a serious disadvantage.