Given we dont really have enough fit midfielders to not play 3 at the back and that Frail is unlikely to change the system, Id go with this (if fit).
Balcombe
Balmer Gordon Casey
Kaleta Thompson
Slattery Miller
Nicholson Maswanhise
Armstrong
If either Miller, Slattery or both arent fit enough then Paton and Halliday will have to do or maybe Andrews. Most important thing though is to get the wing backs pushed right up to support the midfield and keep Ross County pinned back. Nicholson and Maswanhise will have to do a lot of running to support Armstrong. Not much football in the back 3 but I think the SOD / Blaney experiment has run its course.
Id love to see us go 4 at the back with a midfield of Miller, Slattery, Paton, with Nicholson and Maswanhise prividing the width but seems highly unlikely given the circumstances.