Richard Clark wrote:
One
inductance value (however it is wound) is not equivalent everywhere -
hence the proposition of a coil having an equivalent length is rather
preposterous.

Nobody said one inductance value is equivalent everywhere.
In fact, just the opposite is true. The equivalent length
for different coils with the same inductance depends upon
their physical configurations.

For instance, w8ji's loading coil (100t, 10tpi, 2"dia)
calculates to have a VF of 0.0328 while my 75m Texas
Bugcatcher coil with approximately the same inductance
calculates to have a VF of 0.0198, a 66% difference
proving your above premise to be false.

************************************************** *****
THERE IS NO REQUIREMENT THAT TWO COILS WITH THE SAME
INDUCTANCE OCCUPY THE SAME NUMBER OF DEGREES OF ANTENNA.
************************************************** *****

To understand the details, just compare the following
1/4WL resonant stubs:

---25.3 deg Z0=600 ohm---+---10 deg Z0=50 ohm---open

---70.6 deg Z0=100 ohm---+---10 deg Z0=50 ohm---open

Both stubs are electrically 1/4WL = 90 degrees long.

How can 35.3 physical degrees of stub perform a 90 degree
stub function? Hint: There is a 54.7 degree phase shift
at the '+' junction.

Why does the second example require 80.6 physical degrees
of feedline? Hint: There is only a 9.4 degree phase
shift at the '+' junction.

Why does it take 70.6 degrees of Z0=100 ohm feedline
to perform exactly the same function as 25.3 degrees
of Z0=600 ohm feedline?

Both stub segments, Z0=600 and Z0=100, are providing
the same inductance at the '+' junction point, yet
one is 2.8 times longer than the other.

Is "the proposition of a piece of transmission line
having an equivalent length rather preposterous"?
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com