>>10894619I've had to convert a few of those Old Time cars myself (Not the passenger ones but the ones in this picture). I converted them to Micro-Trains couplers using this set
https://www.micro-trains.com/index.php?route=product/product&product_id=365They come with two pairs each so if you have 3 coaches you'd have to buy two sets with one left over.
>>10895060Z is pretty much nonexistent outside of Germany/USA/Japan, and most US railroads favored larger 0-8-0s with tenders and the like for shunting rather than tank engines. Looking around for Japanese Z scale steam I'm only really finding 2-6-4Ts.