Firewall Renforcement?

My buddy has an 88 Mustang 5.0 the one in my profile...Well his tranny has been rebuilt and when he went to pick it up the shop said the firewall was flexing and causing the clutch not to disngauge all the way. Have any of you heard of such a thing? When he presses in the clutch you can kind of see the firewall flex. The guy at the shop said it needed to have the firewall renforced to stop it from flexing and that would allow the clutch to fully disguage...because 1st gear and reverse are hard to get too... the guy said some metal plate would needed to be made but other places said diffrent...What kind of place would he have to take his car too...the tranny place said a bodyshop but a few other places said a custom fab shop...Help us out cause this is geting really annoying and geting worse.