My 79' ScoutII heats up slow too. It max's out at 160 degrees. Runs great and from what I hear the cooler the better. If your concerned check your thermastat or the temp sending unit. As far as your brakes go crawl underneath the truck and check your brake cable it could be broke or loose..
I have a '79 Scout II with similar behavior. I did get the parking brake cable tightened, which helped somewhat. But it still wouldn't hold if I were to rely on it on more than a moderate incline. I just always make sure I park on a reasonably flat surface, and leave it in gear.
This winter in Virginia Beach we've had weather ranging from 27 to 77 degrees in the morning when I head to work. No matter what the temp, it always takes me 10 minutes to warm-up, but then the engine runs strong the whole way in. I use the 10 minutes to listen to the radio, take out the trash, etc... I'd much rather spend 10 extra minutes in my Scout than anytime in an econo-box!