Granted it varies with weight, I have always used 85 KIAS in the long bodies as the "memory" Vbg. 85 KIAS is also what I use for Vx in the long bodies it's one less number to memorize.
In the "generic" airplane in the theory books for a given weight you are at best glide at max L/D. The rate of deterioration (slope) in L/D is less as you move to a faster airspeed than a lower airspeed. So you are penalized less for being a little faster than slower. Some one on the board may have the specific Mooney version of this chart but expect it is similar.
If I must err, I prefer to err on the high side of Vbg for memorized targets, knowing I have fine tuned my glide ring with empirical trials.
Also keep in mind that every Mooney is handmade and differences in fuselage length, rigging etc may have more of an impact that a few knots off the theoretical best answer. Go fly and gather the data for your aircraft.