Was there a option code for factory rust prevention or was it extra sound deadening?
J55 was full undercoating and hood insulation pad.
If the body had been fully under coated prior to this, there would be the chance that the undercoat could be sprayed at the transmission crossmember and rear spring hanger mount locations. This would be a big problem for installing the whole drivetrain, if undercoat was on these mounting points. The trans crossmember is a pretty snug fit, and undercoat at that spot would be a major issue.
If you do a Google search for Dave's Valiant you will see a complete undercarriage picture. The undercoating was kept well away from the trans x-member mounting points.
http://www.ecsautomotive.com/other/As_Bad_As_New.pdf
