There are some things to know about 216s in particular and engines of this era in general. They began their lives in the time before detergent oil. This allowed sludge buildup over time. The sludge often clogged small oil passages like the one that feeds the rocker shaft. This was a big enough problem the after market oiling kets were often installed that bypass the inblock/head passages. You should check these. When detergent oil is used in engines with sludge buildup it can cause the sludge to break loose and clog what wasn't clogged.
The 216 has pressure to the main bearings. The rods are fed through a squirt system that aims a stream of oil to a cup on each rod cap as it rotates. It is a good and dependable system if all is clean and in alignment. Bothe the rod & main bearings are poured babbitt not inserts. They can be converted to full pressure inserts but it can be expensive. One good thing in that new and properly rebuilt 216s had shims in the rod bearings. I don't know about the mains. These shims were there to allow the bearings to be tightened as natural were made then loosen. If you are lucky yours may still have some shims left.
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