5 1/2 h heater core

Alright, I went to the shop to get the heater core replaced on my 1992 5.0L mustang and it took the guy 5 1/2 hours to change the heater core, i personnaly think this is a very long time. I know they have to take the dash appart and my car is equiped with all the ac components but still it seems to be like a long time and i think i got ripped off. I mean the part itself costs 100$ and 5 1/2 hours of labor = 400$. So a total of 500$ plus tax just for that. I may be wrong on this subject and please correct me if i am, i would like to hear your opinions on this since you guys are much more mechanicly inclined then I....so please dont be shy...

Simon

sounds about right,my labor guide says 5.3 hrs. and doesn't include evac. and recharge.