depends where you live - but cb70 / 80 is a beast of an engine!!
just a trick to get one that hasnt been thrashed
but still one of the best engines ever IMHO
bit of exhaust + intake + 12psi boost is a super sweet happy engine that makes that chassis rock!
A cb60 is the single cam carby turbo motor, it will add zip being 50 kw from factory.
If you are handy with a grinder and welder you can use the H series motor, these start from 65 kw from factory and add almost double the torque of the factory cb23.
The hijet version of the cb motor has a different oil pickup due to the motor being slanted to fit. Maybe look at rebuilding your cb23 and add extractors with a freer flowing exhaust, and lightening the flywheel for a bit more zippiness