For those interested I have had a response from Leupold technical re their flips, I already established the Leupold EP flip does fit the March Eypiece (I currently have one on mine) but it doesnt look like the objectives are going to fit - well certainly not at 42mm where I was checking.

To summarise the several emails I have had from Leupold so far:

The thread on the 40mm objective Leupold is:

1.462-48 UNS

Ø1.543" Pitch Diameter = 39.19mm

Ø1.555" Major Diameter

I have looked and the objective diameter of most Leupold 40mm objective scopes seems to be 1.8"

The thread on the 42mm objective Leupold is:

1.875-48 UNS

Ø 1.856" Pitch Diameter = 47.14mm

Ø 1.870" Major Diameter

I have looked and the objective diameter of most Leupold 42mm objective scopes seems to be 2.0"

Now the March objective is 51mm, or near as damn it 2", so as the EP flip fitted I thought a Leup 42mm flip would, but based on these dimensions it seems not?

Not sure why the pitch diameter (I think this is effectively the ID of the thread at the objective?) for the 40mm objective is smaller than the lens but for the 42mm objective its bigger?

For information the only dimension I can easily measure for the March thread is its Pitch Diameter which is 45.25mm.

So it looks like i will have to fit the new March ones when they hit the ground