The LNBF on your Dish 1000 are probably a DPP Twin (119 & 110) and a DP Dual (129) which plugs into the DPP Twin. With this setup, you currently do not need an external switch such as the DP34 or DPP44.
So you are right, you will need a DPP44. Then you will need to remove the 3 cables going into the DPP Twin. Then run 2 cables from the DPP44 to the first 2 Sat Inputs on the DPP44. Then run a cable from the DP Dual to the 3rd position on the DPP44. After you get your Dish 300 (or 500) mounted and peaked, you will connect it to the 4th position. Then you will take the cable(s) from the receiver(s) and connect them to the DPP44 Receiver Output(s). The DPP44 will also need power supplied to the Receiver Port 1, this can be done where the RG6 cable connects to the receiver.
The hardest part will be determining where to mount your Dish 300, which is smaller, even if you are using a Dish 500 with a single DP Dual LNBF. You will need to know where it can be mounted and have a direct line of sight to the 61.5 bird.
Go to the Dish Point Screen for your receiver (Menu, 6, 1, 1).
Select Dish 300, Sat 61.5, enter your correct Zip Code and get the Azimuth.
Then you can use a compass to help determine if you will have line of sight.
I don't know how well it works, but there is a program that will tell you if you have line of sight by using the sun. If you can see the sun at a certain time of day at a particular spot, then you will have a clear line of sight. If you are pretty sure that you have line of sight. Then mount the Dish 300, and then look for the 61.5 by being patient.
I'm sure someone will provide some more info, and if you have more questions, please ask. I personally think it's easy to find and add another satellite orbital location.