L89 is an aluminum headed 396, same as an L78 but heads are aluminum.

The 396 running hard is no surprise, the L78 396 is just a smaller version of the 425 HP L72 427 and the 450 HP LS6 454, all 3 engines have the same heads/cam/intake/carb. The heads flow 290 cfm+, and the stock cam is 242 @ .050. I wasn’t there but some stock L78s were duds from the factory, for exactly the reasons you’d think - big heads, fairly aggressive cam for stock, etc. They came with smog pumps too. Some ran hard. But the potential was there regardless.