I don't know about the Darrin, but the front coils do not need to be removed to change the front shocks on Henry J. I've done it many times. When the nuts are removed, there's a "cup" on the bottom you can tilt out of the way and pull the shock down through the bottom. Compress the new shock, slide it in till it clears the bottom, the tip the cup back into place and tighten the nuts. I'll see if I can find a picture or two of when I did it last.
ADDENDUM: Found the pics. Just remove the top and bottom nut from the shock, compress the shock a bit and tip the cup out from the bottom. See pics of "cup" etc.