Exhaust Pipe--H Box Seperation (UGH!!)

The last and only other time I dropped my engine I made a moderate attempt to seperate my exhaust pipes from the H-box with no luck and ended up taking them away and then re-installing them (the two pipes and the box) as one piece since I had more pressing issues to deal with.



Since then, however, I've procured a much more attractive set of pipes and would love to swap them out with the much grungier ones that refused to cooperate the first time around.



Has anyone ever fought this battle and won?? I'm dealing with an '81 Custom with 75K on the odometer. Heat?? Solvents? I fear getting too heavy handed and trashing the box and/or the pipes that are now on the bike and perfectly funcional.



Thanks, as always, for any thoughts on the matter.....;gweric