We all know and love the Type 97 Chi Ha and Chi Ha Kai, not necessarily for their stats, but because they represent THE most iconic japanese tank of WW2 (with the Ha Go too, maybe). Problem : the regular Chi Ha is a premium you have to buy, and the Chi Ha Kai is an event vehicle that not everyone can get (I did not grind the event to get it, and I didn’t get it with the lootboxes either). And, rightfully so, many people ask for these tanks to be in the regular tree, and so they try to find other japanese tank models with similar stats to replace them as a premium and event vehicle.
What I suggest has probably not been done before (I didn’t see anyone suggest that), but I suggest to replace the premium Chi Ha and the event vehicle Chi Ha Kai with exactly the same models of tanks, but they would still be unique vehicles.
See, I like to browse the internet to find additional stuff to add to Japan, and I came across something when I searched for japanese tanks : there were two hull types for the Chi Has : an early one, and a late one. And ironically enough, these two hull types are already in the game : the premium Chi Ha has the early type, and the event Chi Ha Kai has the late type.
You can see the difference between the two types when you check the rear of both tanks : the EARLY type has grids on each side of the rear, which serve to exhaust the air for cooling the engine, while the LATE type had a different cooling system which did eliminate the grids on each side of the rear of the hull.
The main visual difference, as you can see, are the famous grids, which are inclined and clearly visible on each side of the early type, with the addition of vertical metal plates on top of these, which create an empty space between the plates and the grids. While, the late type however, doesn’t have these grids anymore, and has angled metal plates instead of the grids, which give a continuous silhouette to the hull of the late type, instead of the gaping holes between the grids and the vertical plates found on the early type hulls.
I could find a quote on Wikipedia in japanese, which provides way more details to the tank than the english version. I used google translate so the translation might not be the best :
« The cooling air was sucked in through the intake window on the top of the engine room by two fans attached to the outside of each of the left and right cylinder rows of the engine, and was discharged outside the vehicle through exhaust windows with wind shields on the left and right sides of the rear of the body in the early type body, but in the later type body, the exhaust windows on the left and right sides of the rear of the body were eliminated, and the exhaust was discharged through exhaust windows moved to the back of the left and right sleeves of the rear of the body, improving defense and cooling efficiency. »
If you are interested, it is found in the « Mobility » section of this page :
I found some pictures to show you the difference :
Here you can see the big hole between the horizontal metal plate on the top and the not so visible angled grid inside the space of the early type hull
As you can see here, there are no grids anymore, and the silhouette is continuous, whitout the hole, so it is a late type hull
And the Chi Ha Kai, same deal for these two pictures, as you can notice at the rear of the tanks :
EDIT: I thought I had written it, but I forgot, my bad. 
But anyway, I forgot to mention that the two hull types are already modeled in the game: the ingame Chi Ha has the early type hull, while the Chi Ha Kai has the late type hull. The tank models in Enlisted all come from War Thunder, so you can inspect both in detail if you have that game.
But basically, it would require little effort from the devs: just swap the turrets of the existing tanks, and also swap the shell types along with the turrets, because, the 57 mm and 47 mm shells are different in size/length, so it would require a little update of the internal modules too, but nothing too crazy. I will post pics further down the topic. 
