70 dBA sound level is typical for normal talking in a room.
Any gas powered lawn care machines put out closer to 95 decibels at 10 feet. Much higher noise for the operator. The garbage disposal puts out around 85 dB as does the washing machine or garage door opener.
Either of the engines in question will put out noise greater than 95 dB on stock mufflers. The Saito might sound more pleasant due to being a 4 cycle, but the measured noise would be similar to the 2 cycle.
My best set ups for this displacement size are piped and soft mounted on rubber iso mounts and use noise suppressing APC propellers with high pitch. The best sound I get is 89-90dB at 10 feet. This translates to barely audible at 150 meters distance from the flight line. My flying buds' electric planes of equal power and turning similar sized props are only slightly quieter at 150 meters.
The HOA requirement is ridiculous and should at least be challenged.