Technically you're not getting a 60kWh pack, you're actually getting a software locked 75kWh. Basically they haven't made the 60kWh pack in YEARS. What this means is that even if they do give you a "60" kWh one, you can charge it to 100% daily because 80% of 75kWh is 60, so you wouldn't harm the battery.
You do have another option however, There's a company called "Recell" out of TX that will UPGRADE your battery for a pack anywhere from 64-77kw (210-250 Miles of Range). The pricing is between $7500-$12K and includes shipping your car to their service center in TX AND a 4Yr/50K mile warranty on your reconditioned battery. The shipping back to you is up to $400.00 in the Continental USA, depending on how far you are from them.
Keep in mind however that you're not REALLY getting a new battery with them like you would be with Tesla. What they actually do is to take your existing battery and replace all the high voltage contactors (which had a tendency to burn out on the first gen Model S units) and replace them with "Ludicrous-class" units and then they go through the control boards that don’t meet manufacturer spec are either replaced as needed or have their components upgraded to higher quality components. Considering that you're starting out with just a 60kWh battery pack I'm not sure how that would work, but I guess it wouldn't hurt to give them a call and see what your options are.