Is it possible to install power door locks on a 91 HB, because I took it to a shop to see if they could install them along with an alarm and they said that if the car didn't come with them STOCK then they can not be installed.

Doesn't sound right to me, but...

 

They're full of crap. You can add power door locks to your system, provided it has the outputs. You'll need to purchase the actuators for the locks, and have them installed. Best Buy charges $49 for labor and $30 for the actuator. (times 2 doors). It's not very difficult, but takes some time and precision to get them in. The shop probably didn't want to do it that day. Go to BB. They'll do it for you...