Sorry, been away for most of the day. The factory horn is underneath the car. There is a pan that is roughly between the gas tank and the cabin, that runs along the axis of the front wheels. Jack up the car and there are four bolts to remove to free the pan. The horn is inside there. But if it's aftermarket it could be anywhere.

The blower motor cover is in the trunk. 4 bolts hold it in. It covers the fresh air blower system. It's usually made of some cardboard-like material and is curved along the top.

If you don't feel comfortable chasing down wiring then I'd try to find a reputable person to really remove the alarm system. A poorly removed system can cause a whole bunch of aggravation and misery.

I just recently went through this on my 83 with an aftermarket alarm. Never installed/removed an alarm before so it took me a while fixing one circuit at a time using the factory diagrams. Not difficult, just take your time and be patient.