The basic problem you’re describing here (to which, unfortunately, I don’t have any great solutions to suggest) is sometimes called weight/class inflation. It affects both ships and aircraft, and to some degree it also affects tanks (though in the case of tanks there’s a practical limit on size growth, because once you get over 65-or-so tons, it becomes very difficult for tanks to cross bridges or to travel by railroad).
Weight/class inflation refers to the tendency of warships and warplanes to grow in size and capabilities over the course of time, while still retaining their nominal designation. The F-15, for example, is an air-superiority fighter, but it’s roughly the size of a WWII medium bomber. Similarly, there are modern “destroyers” that are the size of WWII cruisers. And so forth. So a sculpt set ranging from the 1950s to the present is going to be problematic if the size of the sculpts is intended to reflect the nominal designation of each unit (which is the convention used by the A&A OOB sculpts that represent aircraft and surface-combat ships). Unfortunately, it would also be problematic (though in a different way) to use the alternate approach of having the sculpts reflect the physical size of each real-world unit: you could end up with a few extremely large units that would look out of place, and unit type differentiation would have to be based on something other than size.
Perhaps the best approach would be to avoid mixing in a single game units from very different decades. Each decade would have small/medium/large units, and for each decade small medium and large would always more or less correspond to sculpts having uniform sizes of x and y and z…but depending on the decade, a small unit of size x (let’s say, a fighter) would translate into units whose 1950s combat values would be very different from units with 2015 combat values. (For inspiration, have a look at the scene in the movie The Final Countdown in which a pair of F-14 Tomcats get into a dogfight with a pair of WWII Zeros. The Tomcats win – to put it mildly.)