Modulation scheme for simple signal generator
You are trying to build a AM modulator "for alignment".  That apparently means the carrier frequency needs to well known and controlled.

I would use a crystal and digital circuitry to generate the carrier frequency.  You can divide a crystal down to something like 10 kHz, then a PLL to multiply that to whatever frequency you want.  10 kHz is plenty good enough resolution for aligning and calibrating AM radios.

Since this transmitter will be very low power and presumably used where it won't cause interference with other equipment, you don't have to worry about harmonics much.  A amplitude-modulated square wave is much easier to produce than a amplitude-modulated sine wave kept clean of harmonics.

Amplitude modulating a square wave is as simple as clipping the tops to a varying supply voltage.  The result will contain significant signal at the first few odd harmonics, but those will be well out of the band of the radio you are calibrating.  A little R-C low pass filtering after the modulated square wave can cut down on those a bit quite easily.

So don't worry about resonant filters and the like, since those have to be tuned to your particular carrier frequency.  All you have to do is change the divider in the PLL to set the multiple of 10 kHz you want your carrier frequency to be.