http://www.ultracast.ca/products/48/082/installed.html

This website has a picture of a Mk.IX Spinner, with a tape measure on it. I read the length as near enough 25 inches. Perhaps a little less.

How close can you get?

For the time being let us say it is 25 inches.

Add 2 inches for the back plate… a total of 27 inches.

That means the installed length of the ‘Short’ Griffon and the ‘Long’ Merlin, from firewall to front cowling diaphragm are effectively the same.

It will come down to a fraction of an inch.

Mark