Keep the KA pistons and the better compression. Lowering the compression will make the engine a dog any time you are not boosting... which is almost all the time.
Get the front and rear differentials from an earlier '80-'82 720. They are 4.375 and will help mitigate those ratio dropping larger tires.
Guy named Steve ( ]2eDeYe on Ratsun.net https://Ratsun.net https://ratsun.net/admin/?adsess=kmdo9b6ufkb0mpikrpnb72tvui&app... ) makes a beautiful set of powder coated engine brackets for KA swaps. Fitright onto the 720 rubber isolators. That sure makes it easy.
The KA will bolt to your Z24 transmission. Your flywheel, clutch and pressure plate also will bolt on.
Thanks mike. I appreciate all the info. Doing more research i think the turbo ka might be a little much. If I port my z with a Weber 38, 5 thou deck on the head and the nismo cam. Can I get that truck up on the torque a lot? I know hp is limited on it above 130-140. I'm just curious if you gain even more torque. If you can help me out a little, I'd appreciate it deeply. Thank you.