i also built 2 400sbc's for my boat and my oil temp seems real hot,although i have not put a gauge on it.and i have no idea of how hot they were before with the 350's. my best guess is that my hi volume oil pumps carry the oil too fast through the stock oil cooler."heat transfer"i have old cast iron chriscraft oil pans that hold 8 quarts .i'm think of a larger or secondary oilcooler .
i did get a kick out of the other replies
would like to share more info"props/cams/speed/boat/ (buzzardlu12@yahoo.com)