The stock shocks are 13" o.c. eye-to-eye. If you are vertically-challenged, then going w/a shorter shock will allow you to be closer to the ground, but as MaxMidnight said, to preserve balance front to rear, you should remove a like amount on the other end. If you don't, you "slow-down" the steering, making it less-likely to turn, which means, more-effort to get the bike to navigate a corner. Since the VMax is already suspect in the handling dept by a great-many of the unwashed multitudes who also think 40% of the 1985 VMax owners died during their ownership of the bike, because of its shoulder-socket separating thrust, and you certainly don't want to contribute to that statistic, as Mr. Miyagi would have said, "balance in your life." So if you want to reduce the shock height, reduce the front ride height too.
Twelve-point-seven-five inches, assuming you have those stock rear shocks, tells me you probably have the static preload turned-up to the maximum, or close-to it. The general opinion on here is that to go anything more-than an inch-and-a-half in lowering the rear shock will result in much-greater grounding of hard parts as you negotiate curves. In a really-bad scenario, you could deck her undercarriage hard-enough to lever the bike upwards, and possibly enough to lose most or all of your tire contact patch, and there you go, hell-bent upon joining that 40% statistic of first-year VMax owners beyond the Pearly gates, or barbequeing with Mephistopheles, if your path is "the other way" (I hope not!).
If you need to lower the ride height because of your height, I'd suggest one inch shorter rear shocks, a Progressive Suspension front spring kit with a 1" drop, and taking some padding out of the seat, maybe replacing it with a bit more-firm foam, and thick-soled boots to ride.
If you don't need to reduce the ride height, I suggest running the stock 13" shock length in an aftermarket product sized to your riding weight in the spring dept, and buy the best quality one you can afford. ALso, make sure your front forks are running 10-15 psi pressure, and remember that it's NOT a tire, which has much-more volume to fill. A short-time attachment of the air chuck to the fork downtube will quickly air-up the fork, and remember to make sure that your pressure is the same, side to side, which is a 'doesn't concern me' event if you have that balance tube for both sides to be aired-up at the same time. If you don't have air pressure in your front forks, you will be very surprised at how much better the front end feels especially on braking and big hits to the front end suspension, once you have air in there.
Be aware that large changes in suspension lengths will also make your bike more-vertical because of the length of the sidestand, and more-susceptible to tipping-over in a wind (having the bike positioned so that the sidestand is on the 'upwind' side), or on a crowned road. You can have your sidestand cut and welded, or I believe Morley's Muscle sells an exchange-item modded sidestand at a reasonable price.
