I too consulted the conversion chart when I did the Armour - because of the T3 component I find it more powerful as the pig to human ration t4/t3 so I stayed on the lower side to start and yes definitely split dose - this is recommended by manufacturer - I also try not to have any caffeine @ same time I'm taking the Armour or I get a hyper effect immediately.
By the way, you mentioned being in 175 mcg Syntrhoid and still having up and down hypo symptoms with Normal TSH and T4/T3, Have you checked your Cortisol, B12 and Ferretin levels? Because if TSH, T4 and T3 are in good range, maybe there is other problem causing similar Hypo symptoms.
You can try starting at 60 mg (1 grain) for few days and raise it up to 120 mg. I was at 25 mcg levothyroxine and my doc place me at 30 mg, Armour which is a little higher in the conversion chart but did not feel any hyper symptoms other than felt better without brain fog.
The best way to take Armour is dividing your dose in to two or three parts and take them at different times of the day so you get the amount of T3 spread out the day.