How much is a “little money” are you looking to spend?
Are you going to pulling it out and change cam, new pistons some port work or just some bolt on bits to get a little more fun from it.
Most 4k's suffer from restrictive air/fuel into the motor and exhaust out of the motor
So a good cheap starting point would be a set of extractors with a 1 and 3/4 inch exhaust system (not good for a fully worked engine 2" would be better)
A down draft Webber and decent air cleaner, and change the distributor to electronic one from a Liteace motor to give better spark and no more “points” problems
The above list set me back $800 and my KE70’s rwhp from 41 to 62 (motor is also quite fresh only done 20,000km)
I could get a lot more if I change the cam, have the head porting on both the intake & exhaust done, and I can still use the same weber and exhaust I have already invested in.
But as the car is my daily I can’t do with it off the road for that long to get the motor out.