Using equations for feature lengths.

Enter the equations for those part lengths in the assembly. Click on other part's sketch dimensions and feature dimensions while building those equations (unless you like to type).
Keith
PS Beware, if those referenced parts have configurations which change those referenced dimensions, you may have to open and close those parts to get the assembly equations to update properly if you later change configurations of those parts. This may sound a little confusing until you attempt this on a more complex assembly and it does not automatically update the part lengths properly. Someone at Solidworks confirmed that this is how this was supposed to work, but could not explain why. My confusion is I thought the part in memory was the part's dimensions and features used. Multiple Ctrl-Q's do not appear to update the equations also.

If you just want several dimensions to have the same value, then the easiest way is to display all the dimensions using "show feature dimensions" on the annotations folder (in the FM tree). Then select all the required dimensions, right-click and choose "link values" and give it a meaningful name. Et voila....
John H