Regan / Gallagher / Cashelcolane

 Finally found the listing for Griffiths for Castlecolane / Cashelcolane / Cashelcolaun :

There's a lot of Regans and Gallaghers ... likely we are related to all!

The name spelling was part of the problem, as well as the townland moving from Mayo at the time of the Griffith's Evaluation in 1850s to Roscommon in early 1900s.

Map from https://leitrim-roscommon.com/MAPS/ros_par.html

Cashelcolane is part of Castelmore parish, which is #10 in the upper left.

Castlemore map:

https://leitrim-roscommon.com/MAPS/castlemore.html

#9 in upper left is Cashelcolane.

Griffiths only list 4 main plots:

On modern map, you can see the breakout of the plots: