Ich versteh mal wieder nur die Hälfte. 
I do not know any tank title allowing you WWII and modern equipement/scenarios.
The cloosest you can get in combining two era, is SBP, which has early cold war tanks like the Leopard-1A5, T-55, T-62 and M60A3 (the last three only AI-controlled, though), and most modern types like Leopard-2A6, M1A2SEP, T-80U and Challenger-II, which all are crewable except the T-80 (the C2 will become crewable in this winter's major upgrade). You can also tune down the in fluence of modern hightech by disabling certain subsystems like thermal imagers and laser range finders in the mission editor, forcing players tro use classic visual sights with crosshairs and scales like in WWII.
But you should also compare the style of "gameplay" in TvT and SBP. It is very different. I do not know if the Zeewolf mods change that, but the TvT in default status was an arcade shooting gallery with linear and prefixed mission flow, and the player only gunning away, needing to follow the string of mandatory successes before the mission rolled on - else tanks got respawned time and again (hope I get this right, I had only one afternoon on somebody else'S system to testplay it). SBP on the other hand allows you freedom of
mission plan, team cooperation, tactics planning, playing from TC or gunner's seat or as force commander. Making best use of terrain and unit coordination are important parts of the show. You will spend much time i n hte mission planner before mission start. The better your preparation, the better your chances. SBP is no Rambo game. SBP also allows complex mission designs like bridging and minefield breaching operations. Simplified are helicotper and ifantry behavior, with infantry said to be drastically improved with the coming upgrade.
I should, mention that after several years, their major upgrade packages, which usually are very comprehensive, now have become payware (25 dolalrs, I think). Patches are still free. They delivered upgrades for free over the first years. They said from all begining on that at one day they would need to take some minor price for additional content - and they did so after delivering the first 4 years of all patches and upgrades for free.