I have used my Flex 1500 for years on 630m and 2200m. It puts out a nominal 1mW on the transverter port. There is no filtering on TX or RX below about 480kHz. You will need your own preselector on RX and a 500kHz LPF on TX. Then you will need to amplify the 1mw to something useful. I have 50W on 475kHz. It works well, especially on WSPR, OPERA, and WSJT..
The 6500 is great RX below 500 kc at my location if I don't use the 20dB preamp and why would I?Transverter is low output over the full range. Watch out for the transverter port as mine puts out 20dBm into 50ohms. Blew a few MOSFETs the first time.