They list the NTSC version of an old product called the PC/TV by Tecmar. I know the PAL version of this unit converts PAL video to
640x480 VGA at non-interlaced scan (~31 kHz), and the picture looks good. The software drivers have settings that will do interlaced output at RS-170A scan rates, but I have never seen the quality of the picture - YMMV. Perhaps a more modern video capture device could be modified to suit your needs.
The 'simple' answer, is no. Converting PAL 50Hz, to NTSC 50Hz, is relatively simple, and there are several chips to do this. However to convert properly between 50Hz, and
60Hz, requires a framestore, capable of holding several frames (5 minimum), and interpolating these to produce 6 frames out. It is not a simple/cheap project, or something that can be done in a single chip. The development cost of such a unit, would make the price of 'off the shelf' solutions look cheap. Beware though, that some of the cheaper units, do cut corners, and don't give very good results.
I have a Panasonic NV-W1(from 1992) VCR, that can convert from/into anything. But beware these are still expensive used.Samsung makes concurrently a model, I think. You can buy a stand alone converter for