Wade,
Tell your buddy not to go any further without checking out ERA's procedure for setting up the Jag rear-suspension assembly for use in their cars. Click on the following to check it out:
http://www.erareplicas.com/427/shorten.htm
As for bump/droop, they are also called jounce and rebound, or wheel travel up and then down from curb height. Sometimes these terms are called compression and extension, but these travels are all the same regardles of what you call them.
Jounce (bump) travel is typically three to four inches with rebound (droop) being about the same or slightly more.
I recommend that your buddy consider purchasing ERA's subframe for retrofitting the Jag setup into his car. E-mail or call them for dimensions to make sure it's possible to mate the two.
