I think serenade is deeper than friendship 7, so I'd guess you want 28-1/2" legs for serenade.

if you assume:
- the front rail should be around 35-36 inches off the floor
- the typical leg is around 3" from the top to the center of the top hole
- your cabinet distance from top of rail to center of top hole = X

then the leg length would be 36 - X + 3, not counting the levelers, so whatever number you get pick a standard leg length less than that.

if you don't have another game handy to check, hopefully someone can measure their game and see if 39 - X is about right.