On my conversion I used a Professional Products #80007 damper:

http://www.professional-products.com/da … SBford.php

It’s the same length as the 5 bolt 260/289 damper, has 50 oz imbalance, it’s drilled for both 3 and 4 bolt pulleys, and has etched and painted-in timing marks to suit pretty much any of the different front cover timing mark locations. I haven’t run it yet but it’s definitely one of the most ideal parts for the job. If you’re looking at racing then they also have SFI approved versions of the same damper.