[HO455]

Well it hard to tell from the photos if you have the short water pump or not. If you've have the short water pump then that cast 3 groove pulley with the built in spacer would need to be swapped for a stamped steel version with no spacer.

What transmission is hooked to your SBC? Is it the stock engine/transmission combination? If not it is possible that they need to slide back.

Your new engine is looking good.

Here is a reference to fan spacing from Flex-a-Lite.

If you have a fan shroud, the position of the fan blades in the shroud is very important to maximize airflow. Looking from the side of the engine, the fan blades should be half in and half out of the shroud. If the fan is too far inside of the shroud, it won’t pull as much air through the shroud as it could. Instead it will create turbulence inside the shroud, spinning the air, but not efficiently pulling it through. If the blades are not far enough inside the shroud, the fan will pull air from around the shroud rather than through it.

https://flex-a-lite.com/blog/the-per...20engine%20rpm.