I really like my Leece-Neville 90 amp marine alternator. It was very reasonably priced ($167 2 years ago, if I recall correctly). I think that you should be careful to not put too big an alternator load on your small engine, though. 45-50 amps is probably the absolute maximum that your 7 HP could power. I think 70 amp would be too much for 7 HP.
I think the JC Whitney marine looks like a fair price. It might be worth a try.
1983 Ericson 33
Channel Islands, California