The Cyclone Gt will handle a wide range block so if you do not mind wider gaps you could install a freewheel with lower gearing and see if that works and leave the SR crank intact.

Have converted doubles to triples using longer stack bolts and spacers which is an old fashioned solution to get lower gearing on a road double with no provision for a granny... you will need a longer crank spindle for this in most cases.