All of Professional Products' SB Ford Dampers are all made to the 1963-'69 length. This allows the use of both early and late style dampers in early chassis. All SB Ford dampers also have both the three and four bolt pulley patterns. They also have three sets of timing marks to suit all SB engines. If your stock damper is longer than three inches, we make up the difference with a series of spacers. To determine which spacer you need, measure the length of your damper and refer to the chart to see which spacer you need. Our standard spacers are made of aluminum and are very inexpensive. If you have a 5.0L engine running a belt driven blower, we recommend that you use our 81009 Steel Spacer instead of the 81007 aluminum one. See below:

289/302/351W from 1963-1969 - 3.050" Damper Length - No Spacer Required
351W/351C/400M from 1969-1980 - 3.400" Damper Length - Use #81006 Spacer (.350")
351 HO (351W) from 1991-UP - 3.875" Damper Length - Use #81008 Spacer (.875")
351W/302 from 1980-UP - 3.875" Damper Length - Use #81008 Spacer (.875")
302/5.0L from 1970-1996 - 3.950" Damper Length - Use #81007 Spacer (.950")
351W from 1980-1996 - 3.950" Damper Length - Use #81007 Spacer (.950")

Notes: Remove .070" off rear of damper if Ford .917" Crank Sprocket is used. A 3.187" damper length may have been used on some of the listed applications. This requires spacer modification. See modifications shown in instructions that come with the damper.