up-down-cross mini converter - NTSC output?

Will it convert HD SDI to NTSC SDI?
The spec sheet says it will convert any HD to SDI and reverse, but the listed outputs are only HD.
Can it output NTSC?

And secondly, are the options to crop or letterbox the 16:9 to 4:3 conversion?

You need a converter such as the Teranex Mini Analog to SDI 12G Converter. That will convert SDI to NTSC/PAL.