Thanks for the ideas!
I ran some more simulations; attached are the FFTs of a 70Vpp sine wave after rectification as well as that same waveform put through my filter.
Jim, you are certainly correct about the higher frequency harmonics. I realize that after looking at the FFTs. This gives some great information but still, my 5dB figure does not match up.
Mike, I modeled my source and load impedances with resistors, and they are included in my transfer function as R_s and R_l. However, I don't think I've given the equivalent impedance of the diodes a fair characterization. When I stick a source impedance of 2-3 ohms (instead of 0.1) into my transfer function (R_s), the resulting magnitude response matches up a little nicer.
I plan to run some more simulations and hopefully use some sort of buffer to eliminate the diodes from the equation.
My ultimate goal is to arrive at an expression that will estimate output ripple at full power supply load using this CLC topology. The source and load will remain modeled as resistors. From what I've seen so far, you can save some money by using this topology with a rather large inductor. For example, letting C=4800uF and L=4.7mH produces 0.8% ripple under a 3A load. Producing this result with a single capacitor alone would require something on the order of 40,000 uF. Furthermore, it's better than an RC rectification filter because, in that case, there is significant ohmic loss.