Tiny point of order.
The Buick 300cid (evolved from the 215 aluminum v-8 in 1960) is not a Nailhead.
The Nailhead engines are a different beasty altogether.
The 300 V-8 have "vertical" valve covers and has similar appearance and I think that has led to the continued use of "300 (or even 301) Nailhead. (yours do not have the appearance of being vertical)
I have had three Buicks with the 300 and I like them for the little gusty engines they can be.
It's a fun thing to drive the 300 and the ST300 with switch pitch.
Let me go find some pics of the valve covers. BRB...

This is the nailhead with valve covers and intake and valley cover removed.
Notice the intake ports are horizontal and the valves are vertical.

This is a 215 V-8, that is pretty close to what the 300 looks like. (I could not find a good pic of a 300 with the valve covers and intake to compare to a nailhead)
The intakes are angled, not horizontal, and the valves are angled, not vertical.
The valve covers on the 300 are a trapezoid cross section, and that gives the illusion that the 300 head is like a nailhead. The nailhead covers are pretty much square cross section.