Just came across this after searching on Google for Beinn Fhionnlaidh from Iron Lodge. I regretfully missed it out too some years ago so am thinking of walking in from Iron lodge and also climbing Mullach na Dheirgain and Sgurr nan Ceathreamhnan on the same day, weather permitting! I found this which may interest you:
http://www.scottishhills.com/html/modules.php?name=Forums&file=viewtopic&t=8417
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