I know that these turtles use a lens focus driven by a wheel from the outside instead of a bellows and rails. I also know that ground glass focusing is available for this purpose with either of the original two backs.

Was there any kind of rangefinder for these or were photographers expected to pop up a tripod and focus on the glass and pray nothing moved or figure the hyperfocal range and pray everything stayed in range?

The reason I'm asking is that I've got one that some monster in the dark past modified with a Graflok back and I think it would be really handy to add a 120 roll film back... but the focusing issue seems a problem

And I like trying to solve problems.

I use a little pocket range finder in feet when I cannot use the hyperfocal.
Like this:
http://www.ebay.fr/itm/Vintage-Hugo-Meyer-Pocket-Range-Finder-Made-in-U-S-A-/251350300284?pt=LH_DefaultDomain_0&hash=item3a85a5367c

Cheers,
Laurent
My Combat : https://www.facebook.com/laurent.demiollis/media_set?set=a.4510969618138.148558.1407554840&type=3

What a great idea, I had forgotten that those existed!