Engine mounts will be different. Remove the ones off your 3K and attach to 4K.
Lose the pollution gear and use the carb off the 3K. Put a kit through it, or fit a Weber. (Alot of people in here use them, I don't, I'm not a fan)
Don't ever put a used timing chain on another engine. Buy a new two row, they're not that expensive. 3k head will bolt onto a 4K. Wiki has more info.
I also haven't had much success with electronic ignition on my race motors. I still use points and have no issues with them. They came on 5K engines and some import 4K's. Call someone like Just Jap.
Power increase by a straight change over will not be great.
There is a good "how to" bit in the wiki.
R