I have not read the book, "Ethics in Early Buddhism", or anything (that I recall) of substance from David Kalupahana. This review makes me want to read it (eventually) just to see what NOT to do in my own work. I recall being warned to be wary of Kalupahana's ideas by Paul Williams in Bristol as well.
The review is in The Journal of Religion, Vol. 77, No. 2 (Apr., 1997), pp. 337-340