Take the basic Pnzer Mk IV (F2/G and above) and put the 75mm L48 (I think that the gun it ended the war with, but if that is not available, 75mm L40). From there, immediately introduce "skirts", as well as giving all the the relevant pieces of armor beneath the "Skirts" a sloped face. For the armor, I would say something like 75mm turret with sloping similar to the Panther, with 80mm on the front body, also sloped, and standard armor thickness on the rest of the Mk IV. This is made from a logistical standpoint, wherein you have plenty of very good tanks out on the field, rather than a few awesome tanks that still need work (Panther, Tiger, etc.). If this doesn't work, someone has to come up with the plans for the Hetzer Tank destroyer. Its gun can knock out all but the most heavily armored foes from the front (or maybe it was from various angles, my books aren't with me), its simple to produce, has a low profile, and is fast.