Seems my Paper-panzer efforts are crossing my IJA efforts: I've seen mention of IJA late war plans to upgrade the Type 5 Chi-Ri medium tank to an 88mm of a German design.
Does anyone know if this would have been the Tiger II
KwK 43 L/71 or the KwK 36 L/56 of the Tiger I

https://tanks-encyclopedia.com/ww2/jap/Type_4_Chi-To.php

https://en.wikipedia.org/wiki/Type_5_Chi-Ri_medium_tank

https://www.hlj.com/1-35-scale-type-4-chi-to-prototype-version-fnmfm-32
This could be a starting point, swap the gun for an 88, possibly extend the turret backwards for weight balance and increased space for recoil. Don't know if it is still in production though ...

Amusing Hobby have this one, more of Ferdinand/Elephant approach ....

Recently, or soon to be, released.

/ Robin

Japanese 88 m AA-gun which was a reverse engineered
German SK C/30 88 mm gun (not to be confused with the
famous 88 mm)

https://en.wikipedia.org/wiki/Type_99_88_mm_AA_gun

https://en.wikipedia.org/wiki/8.8_cm_SK_C/30_naval_gun

Moved from Modeling in General

Not much sense in starting with the Ho-Ri I or II since both projected variants would have mounted a 105mm gun, not an 88mm. And I am not sure why you would mention the Type 4 Chi-To - completely different vehicle that mounted the 75mm, not an 88mm.

But you are correct in that the anticipated 88mm gun that was planned to be used in the Type 5 Chi-Ri was to have been based on the Type 99 88mm AA gun. Which would mean that the barrel length would likely have been shorter then the 75mm Type 5 gun used on the prototype Type 5 Chi-Ri. You can clearly see how short the 88mm barrel is in the links you provided, especially in comparison to the 75mm used in the Type 5. Turret modifications other then the gun trunnions perhaps, would not have been necessary.

As an aside, the Brave Model 1/35 resin kit of the Chi-Ri actually includes turned metal barrels of both the 75mm and 88mm guns. Only the barrel is different, nothing else, and it is indeed shorter then the 75mm as per the Type 99. Very rare kit (even inside Japan) released about 15 years ago.