If you are in love with the "classic" look of the old Islander, go for it. Pending survey and appropriate pricing, of course. Pisces diesels were common on lots
of 70's boats -- being marinized Isusu diesels, and very long-lived if maintained. Note that any search on this brand on the 'net will turn up sailors seeking parts... which is often a problem with really old engines.
The Pearson is a much more "modern" design and will have better resale value some day, and should be a better sailing boat, as well.
It is all about "Choices and options".