Good luck getting any resolution. As you now know you should never expect the seller to be totally honest about somethings and that you should confirm the condition of the truck yourself before bidding or bid accordingly. Congrats on your truck though. The cab corners are not too hard to do yourself if you have the tools. If not then any repair on these old truck will put a significant dent in the wallet.
The wiper motor is vacuum operated as you probably know. They can be rebuilt or replaced with an electric motor which is what I plan to do. The rebuild information can be found doing a search here on the bolt.
The parking brake is a bigger challenge as it sounds like the arm that goes from the pedal assy to the rear cross bar is missing. I think these are available from the suppliers but they are not cheap. You might find one on the swap meet also. Are the brake cables from the crossbar to the rear drums in place? If not they will be needed also. If you do not have it yet, you will need to get the factory assembly manual. It can be found on ebay or from the various suppliers.
As for professional repair of the brake assy, it may be hard to find someone familar with the old truck. The average labor rate for mechanics is about $65/hr in this area.
As an old truck owner you should be willing to work on it yourself. If that is not what you wanted to do then a totally restored truck may have been a better choice. You might consider selling it now and looking for another option. Good luck.
