the bolts should come out, they can get rusted/stuck in place due to the environment they are in.  couple tricks you can try are heat them up with a propane torch then let cool, this will sometimes break the rust bond.  also rap on them with a hammer that will do the same thing.  spraying lube doesnt do much as it cant get to the threads very well when the bolt is tightened.  use a good wrench or socket so you dont round the heads of the bolt. also try a swivel & extension to get on the bolt then use an impact gun, the shocking forces will usually break it free... or bust the bolt head off to allow to remove the plate & tubes & hopefully leave enough of the bolt to grab onto or weld a nut to remove.  good luck!