Hmm, you may have FH-6207 hub then, 6-spd. Measure the overall outside width of the 7-spd cassette you have, the spacers look a little wide. If you don't mind using friction-shifting, I have fitted 7-spd cassettes on 6-spd freehubs by grinding down the spacers. Hold them loosely in your hand and place the side on rotary grinder wheel. The grinder will spin the spacer through your hand as it takes off a little at a time. Do it gradually and measure with calipers often. The 7-spd spacers should be 3.1mm for metal, 3.15mm for plastic ones. You can reduce them to 3.0mm for 8-spd spacing and the 7th cog should be on in regular orientation. Also grind the built-in spacer on that 1st cog as well.
Good luck!