Groves came in both hunting and target model recurves in various lengths. If your Groves is a 62" hunting recurve, try a brace height between 7"-8".
When I was much younger, the 62" Magnum II hunting recurve I shot, the sweet spot was between 7 1/2"-8" depending on what aluminum arrow and point weight I was shooting at the time.
With the above stated, keep in mind I have a 30" draw length.
The 62" target models, the sweet spot was usually between 8"-8 1/2", but these recurves didn't come in heavy poundages so if your bow is 64#, I would first try the 7"-8" brace height.