318 timing chain.....and why the engine should come out.

It's "good" to not just change the bearings, because the crank journals will most likely be worn and 'contoured' to the old bearings.
Installing new ones would likely cause the new ones to wear double the speed they would normally do.
A highvolume pump on an old worn engine is usually good insurance to get some more years of service out of it.
But the oilpressure-gauge will usually tell the story here.