Many SBC had 3" pipes, easy enough to tell or convert to 4" with new risers. Both my Scarab and my Baja had slash cuts. The internal flappers burn out pretty fast so be carefull with water intrusion if you anchor often. I got tired of them and cut the tips straight and put Salisbury flaps on them...no more worries. With the Donzi I have Capt'n call and I just set it to quiet when I anchor offshore that way no water can flush back up my pipes, even though I have flaps as well.
Nick
1994 22' Classic-454 B1 Red & white
1981 13' Whaler sport(original owner)
South Tampa Bay, FL "May I mamoo dogface to the banana patch?"