What Load impedance to use for LC Filter before transformer?
You use the reflected version from high to low. You turns ratio is 10:1 so the 100 ohms on the secondary will appear as 1 ohm on the primary.

But, you mention low pass filtering the 60 Hz - stay as far from the 60 Hz as you can because although the Ls and Cs you have drawn make a low pass filter, at resonance they are series resonant and will act as almost a dead short. The resonant frequency is: -

\$\dfrac{1}{2\pi\sqrt{LC}}\$ Hz where L = L1 + L2 and C = C1 + C2

Just be aware of this in order to avoid burning stuff!!!