Hi J, it's less about horsepower and more about how the vehicle is used. For a street driven car, we would recommend either 19 or 25, but probably no larger, and with a thermostatic plate. Even the thermostatic adapters will allow some oil to pass through, so having an adapter too large can cause it to run too cool and not reach operating temperature.

Yes, but you'll want to replace the block plugs in the block (where the tree mounts to) with the relief valves from the NA (p/n 15241-40F00)