Your calcs and method look fine to me. You came out with the same conversions you see here
and in wikipedia for converting CaCO3 equivilents to Ca++, Mg++, and HCO3- ion.
Your method is nice because it is from scratch, and carefully shows cancelling of units in the conversions.
FWIW, note that you could have gotten to your result faster by using a commonly used unit conversion factor to get you from "as CaCO3" to molar concentrations and vice versa:
100 mg/l (or ppm) CaCO3 equivalent = 1 mmole/l of divalent ion or compound
50 mg/l (or ppm) CaCO3 equivalent = 1 mmole/l of univalent ion or compound
(mmol is millimole, 1/1000th of a mole)
These factors are good to 3 decimal places. (If you wanted silly precision you would use 100.0869 (the molar mass of CaCO3) and 50.04345 .)
One reason the unit "as CaCO3" is handy is because it's easy to divide by 100. Often you can do these in your head - divide by 100, then if it's univalent multiply by 2.
Divalent ions and compounds include Ca++, Mg++, CaCl2, MgSO4, MgSO4*(7H20), CO3--, SO4-- ....
Univalent would include HCO3-, Na+ , K+, NaHCO3, KHCO3, Cl- .....
So you can plug in conversion factors like 1 mmol NaHCO3 / 50 mg CaCO3 equivalent
to quickly get your calculation into moles.
For your example:
60 mg/l CaCO3 equivalent * (1 mmol/l NaHCO3 / 50 mg/l CaCO3 equivalent) = 1.2 mmol/l NaHCO3
1.2 mmol/l NaHCO3 * ( 84 mg NaHCO3 / 1 mmol NaHCO3) = 101 mg/l NaHCO3
for the 200x concentrate,
101 mg/l * 1g/1000mg * 200 = 20.2 g/l (same as your result)
Note: Another common way to do this would be to use chemical equivalents
50 mg/l (or ppm) CaCO3 equivalent = 1 milliEquivalent/l of any compound. Then convert to mmol using 2 mEq/mmol for divalent and 1 mEq/mmol for univalent ions and compounds.